Infancy and Toddlerhood

Why understand human development during infancy?

An infant laying in a blanket smiling

Welcome to the story of development from infancy through toddlerhood; from birth until about two years of age. Did you ever wonder how babies grow from tiny, helpless infants into well-developed and independent adults? It doesn’t happen overnight, but the process begins right from day one. Infancy is a time when tremendous growth, coordination, and mental development occur. Most infants learn to walk, manipulate objects, and can form basic words by the end of infancy. By 5 months a baby will have doubled its birth weight and tripled its birth weight by the first year. By the age of 2, a baby’s weight will have quadrupled!

Researchers have given this part of the life span more attention than any other period, perhaps because changes during this time are so dramatic and so noticeable. We know that much of what happens during these years provide a foundation for one’s life to come, however, it has been argued that the significance of development during these years has been overstated (Bruer, 1999). Nevertheless, this is a period of life that contemporary educators, healthcare providers, and parents have focused on quite heavily. It is also a time period that can be tricky to study—how do we learn about infant speech when they cannot articulate their thoughts or feelings? For example, through research we know that infants understand speech much earlier than their bodies have matured enough to physically perform it; thus it is evident that their speech patterns develop before the physical growth of their vocal cords is adequate to facilitate speech.

In this module, we will examine the rapid physical growth and development of infants, look at the influences on physical growth and cognitive development, then turn our attention toward emotional and social development in the early years of life. The early years are a time of rapid physical, cognitive, social, and emotional development, which have a direct effect on a baby’s overall development and the adult they will become.

What you’ll learn to do: describe physical growth and development in infants and toddlers

A closeup of an infant's feet

We’ll begin this section by reviewing the physical development that occurs during infancy, a period that starts at birth and continues until the second birthday. We’ll see how this time involves rapid growth, not only in observable changes like height and weight but also in brain development.

Next, we will explore reflexes. At birth, infants are equipped with a number of reflexes, which are involuntary movements in response to stimulation. We will explore these innate reflexes and then consider how these involuntary reflexes are eventually modified through experiences to become voluntary movements and the basis for motor development as skills emerge that allow an infant to grasp food, rollover, and take the first step.

Third, we will explore the baby’s senses. Every sense functions at birth—newborns use all of their senses to attend to everything and every person. We will explore how infants’ senses develop and how sensory systems like hearing and vision operate, and how infants take in information through their senses and transform it into meaningful information.

Finally, since growth during infancy is so rapid and the consequence of neglect can be severe, we will consider some of the influences on early physical growth, particularly the importance of nutrition.

Learning outcomes

  • Summarize overall physical growth patterns during infancy
  • Describe the growth of the brain during infancy
  • Explain gross and fine motor skills in infants
  • Explain newborn perceptual abilities
  • Explain the merits of breastfeeding
  • Discuss the importance of nutrition to early physical growth, including nutritional concerns for infants and toddlers such as marasmus and kwashiorkor
  • Describe sleep concerns for infants
  • Explain the vaccination debate and its consequences

Physical Growth and Brain Development in Infancy

Overall Physical Growth

By the time an infant is 4 months old, it usually doubles in weight, and by one year has tripled its birth weight. By age 2, the weight has quadrupled. The average length at 12 months (one-year-old) typically ranges from 28.5-30.5 inches. The average length at 24 months (two years old) is around 33.2-35.4 inches (CDC, 2010).

A collage of four photographs depicting babies is shown. From left to right they get progressively older. The far left photograph is a bundled up sleeping newborn. To the right is a picture of a toddler next to a toy giraffe. To the right is a baby blowing out a single candle. To the far right is a child on a swing set.
Figure 1. Children experience rapid physical changes through infancy and early childhood. (credit “left”: modification of work by Kerry Ceszyk; credit “middle-left”: modification of work by Kristi Fausel; credit “middle-right”: modification of work by “devinf”/Flickr; credit “right”: modification of work by Rose Spielman)

Monitoring Physical Growth

As mentioned earlier, growth is so rapid in infancy that the consequences of neglect can be severe. For this reason, gains are closely monitored. At each well-baby check-up, a baby’s growth is compared to that baby’s previous numbers. Often, measurements are expressed as a percentile from 0 to 100, which compares each baby to other babies the same age. For example, weight at the 40th percentile means that 40 percent of all babies weigh less, and 60 percent weigh more. For any baby, pediatricians and parents can be alerted early just by watching percentile changes. If an average baby moves from the 50th percentile to the 20th, this could be a sign of failure to thrive, which could be caused by various medical conditions or factors in the child’s environment. The earlier the concern is detected, the earlier intervention and support can be provided for the infant and caregiver.

Body Proportions

Another dramatic physical change that takes place in the first several years of life is a change in body proportions. The head initially makes up about 50 percent of a person’s entire length when developing in the womb. At birth, the head makes up about 25 percent of a person’s length (just imagine how big your head would be if the proportions remained the same throughout your life!). In adulthood, the head comprises about 15 percent of a person’s length. Imagine how difficult it must be to raise one’s head during the first year of life! And indeed, if you have ever seen a 2- to 4-month-old infant lying on their stomach trying to raise the head, you know how much of a challenge this is.

The Brain in the First Two Years

Some of the most dramatic physical change that occurs during this period is in the brain. At birth, the brain is about 25 percent of its adult weight, and this is not true for any other part of the body. By age 2, it is at 75 percent of its adult weight, at 95 percent by age 6, and at 100 percent by age 7 years.

Brain MRIs that show similar regions activated by adult brains and infant brains while looking at either scenes of faces.
Figure 2. Research shows that as early as 4-6 months, infants utilize similar areas of the brain as adults to process information. Image from research article conducted by Ben Deen, Hilary Richardson, Daniel D. Dilks, Atsushi Takahashi, Boris Keil, Lawrence L. Wald, Nancy Kanwisher & Rebecca Saxe.”Article OPEN Published: 10 January 2017
Organization of high-level visual cortex in human infants”. Image retrieved from

Communication within the central nervous system (CNS), which consists of the brain and spinal cord, begins with nerve cells called neurons. Neurons connect to other neurons via networks of nerve fibers called axons and dendrites. Each neuron typically has a single axon and numerous dendrites which are spread out like branches of a tree (some will say it looks like a hand with fingers). The axon of each neuron reaches toward the dendrites of other neurons at intersections called synapses, which are critical communication links within the brain. Axons and dendrites do not touch, instead, electrical impulses in the axons cause the release of chemicals called neurotransmitters which carry information from the axon of the sending neuron to the dendrites of the receiving neuron. 

While most of the brain’s 100 to 200 billion neurons are present at birth, they are not fully mature. Each neural pathway forms thousands of new connections during infancy and toddlerhood. During the next several years, dendrites, or connections between neurons, will undergo a period of transient exuberance or temporary dramatic growth (exuberant because it is so rapid and transient because some of it is temporary). There is a proliferation of these dendrites during the first two years so that by age 2, a single neuron might have thousands of dendrites. After this dramatic increase, the neural pathways that are not used will be eliminated through a process called pruning, thereby making those that are used much stronger. It is thought that pruning causes the brain to function more efficiently, allowing for mastery of more complex skills (Hutchinson, 2011). Transient exuberance occurs during the first few years of life, and pruning continues through childhood and into adolescence in various areas of the brain. This activity is occurring primarily in the cortex or the thin outer covering of the brain involved in voluntary activity and thinking. 

Parts of a neuron, showing the cell body with extended branches called dendrites, then a long extended axon which is covered by myelin sheath that extends to the synapses.
Figure 3. Parts of a neuron.

The prefrontal cortex, located behind the forehead, continues to grow and mature throughout childhood and experiences an additional growth spurt during adolescence. It is the last part of the brain to mature and will eventually comprise 85 percent of the brain’s weight. Experience will shape which of these connections are maintained and which of these are lost. Ultimately, about 40 percent of these connections will be lost (Webb, Monk, & Nelson, 2001). As the prefrontal cortex matures, the child is increasingly able to regulate or control emotions, to plan activity, to strategize, and have better judgment. Of course, this is not fully accomplished in infancy and toddlerhood but continues throughout childhood and adolescence.

Another major change occurring in the central nervous system is the development of myelin, a coating of fatty tissues around the axon of the neuron. Myelin helps insulate the nerve cell and speed the rate of transmission of impulses from one cell to another. This enhances the building of neural pathways and improves coordination and control of movement and thought processes. The development of myelin continues into adolescence but is most dramatic during the first several years of life.

Motor and Sensory Development

From Reflexes to Voluntary Movements

Every basic motor skill (any movement ability) develops over the first two years of life. The sequence of motor skills first begins with reflexes. Infants are equipped with a number of reflexes, or involuntary movements in response to stimulation, and some are necessary for survival. These include the breathing reflex, or the need to maintain an oxygen supply (this includes hiccups, sneezing, and thrashing reflexes), reflexes that maintain body temperature (crying, shivering, tucking the legs close, and pushing away blankets), the sucking reflex, or automatically sucking on objects that touch their lips, and the rooting reflex, which involves turning toward any object that touches the cheek (which manages feeding, including the search for a nipple). Other reflexes are not necessary for survival, but signify the state of brain and body functions. Some of these include the Babinski reflex (toes fan upward when feet are stroked), the stepping reflex (babies move their legs as if to walk when feet touch a flat surface), the palmar grasp (the infant will tightly grasp any object placed in its palm), and the Moro reflex (babies will fling arms out and then bring to the chest if they hear a loud noise). These movements occur automatically and are signals that the infant is functioning well neurologically. Within the first several weeks of life, these reflexes are replaced with voluntary movements or motor skills.

Motor development

Motor development occurs in an orderly sequence as infants move from reflexive reactions (e.g., sucking and rooting) to more advanced motor functioning. This development proceeds in a cephalocaudal (from head-down) and proximodistal (from center-out) direction. For instance, babies first learn to hold their heads up, then sit with assistance, then sit unassisted, followed later by crawling, pulling up, cruising, and then walking. As motor skills develop, there are certain developmental milestones that young children should achieve. For each milestone, there is an average age, as well as a range of ages in which the milestone should be reached. An example of a developmental milestone is a baby holding up its head. Babies on average are able to hold up their head at 6 weeks old, and 90% of babies achieve this between 3 weeks and 4 months old. If a baby is not holding up his head by 4 months old, he is showing a delay. On average, most babies sit alone at 7 months old. Sitting involves both coordination and muscle strength, and 90% of babies achieve this milestone between 5 and 9 months old (CDC, 2018). If the child is displaying delays on several milestones, that is a reason for concern, and the parent or caregiver should discuss this with the child’s pediatrician. Some developmental delays can be identified and addressed through early intervention.

Link to Learning

It is important to understand that there is a range of normal for reaching developmental milestones.  It should not be a competition between parents whose child reached which milestones first. Each child will develop at their own pace based on many different factors. However, if a delay is diagnosed there are early invention services that are available in most states.  Review the services that are available in Arizona.

Gross Motor Skills

Baby grabbing a leaf
Figure 4. This baby is working on his pincer grasp.

Gross motor skills are voluntary movements that involve the use of large muscle groups and are typically large movements of the arms, legs, head, and torso. These skills begin to develop first. Examples include moving to bring the chin up when lying on the stomach, moving the chest up, rocking back and forth on hands and knees. But it also includes exploring an object with one’s feet as many babies do, as early as 8 weeks of age, if seated in a carrier or other device that frees the hips. This may be easier than reaching for an object with the hands, which requires much more practice (Berk, 2007). And sometimes an infant will try to move toward an object while crawling and surprisingly move backward because of the greater amount of strength in the arms than in the legs!

Fine Motor Skills

Fine motor skills are more exact movements of the hands and fingers and include the ability to reach and grasp an object. These skills focus on the muscles in the fingers, toes, and eyes, and enable coordination of small actions (e.g., grasping a toy, writing with a pencil, and using a spoon). Newborns cannot grasp objects voluntarily but do wave their arms toward objects of interest. At about 4 months of age, the infant is able to reach for an object, first with both arms and within a few weeks, with only one arm. Grasping an object involves the use of the fingers and palm, but no thumbs. Stop reading for a moment and try to grasp an object using the fingers and the palm. How does that feel? How much control do you have over the object? If it is a pen or pencil, are you able to write with it? Can you draw a picture? The answer is, probably not. Use of the thumb comes at about 9 months of age when the infant is able to grasp an object using the forefinger and thumb (the pincer grasp). This ability greatly enhances the ability to control and manipulate an object, and infants take great delight in this newfound ability. They may spend hours picking up small objects from the floor and placing them in containers. By 9 months, an infant can also watch a moving object, reach for it as it approaches, and grab it. This is quite a complicated set of actions if we remember how difficult this would have been just a few months earlier.

Table 1. Timeline of Developmental Milestones.
~2 months
  • Can hold head upright on own
  • Smiles at sound of familiar voices and follows movement with eyes
~3 months
  • Can raise head and chest from prone position
  • Smiles at others
  • Grasps objects
  • Rolls from side to back
~4-5 months
  • Babbles, laughs, and tries to imitate sounds
  • Begins to roll from back to side
~6 months
  • Moves objects from hand to hand
~7-8 months
  • Can sit without support
  • May begin to crawl
  • Responds to own name
  • Finds partially hidden objects
~8-9 months
  • Walks while holding on
  • Babbles “mama” and “dada”
  • Claps
~11-12 months
  • Stands alone
  • Begins to walk
  • Says at least one word
  • Can stack two blocks
~18 months
  • Walks independently
  • Drinks from a cup
  • Says at least 15 words
  • Points to body parts
~2 years
  • Runs and jumps
  • Uses two-word sentences
  • Follows simple instructions
  • Begins make-believe play
~3 years
  • Speaks in multi-word sentences
  • Sorts objects by shape and color
~4 years
  • Draws circles and squares
  • Rides a tricycle
  • Gets along with people outside of the family
  • Gets dressed
~5 years
  • Can jump, hop, and skip
  • Knows name and address
  • Counts ten or more objects


Link to Learning

The Centers for Disease Control and Prevention (CDC) describes the developmental milestones for children from 2 months through 5 years old. After reviewing the information, take the CDC’s Developmental Milestones quiz to see how well you recall what you’ve learned. If you are a parent with concerns about your child’s development, contact your pediatrician.


Good nutrition in a supportive environment is vital for an infant’s healthy growth and development. Remember, from birth to 1 year, infants triple their weight and increase their height by half, and this growth requires good nutrition. For the first 6 months, babies are fed breast milk or formula. Starting good nutrition practices early can help children develop healthy dietary patterns. Infants need to receive nutrients to fuel their rapid physical growth. Malnutrition during infancy can result in not only physical but also cognitive and social consequences. Without proper nutrition, infants cannot reach their physical potential.

Introducing Solid Foods

Breast milk or formula is the only food a newborn needs, and the American Academy of Pediatrics recommends exclusive breastfeeding for the first six months after birth. Solid foods can be introduced from around six months onward when babies develop stable sitting and oral feeding skills but should be used only as a supplement to breast milk or formula. By six months, the gastrointestinal tract has matured, solids can be digested more easily, and allergic responses are less likely. The infant is also likely to develop teeth around this time, which aids in chewing solid food. Iron-fortified infant cereal, made of rice, barley, or oatmeal, is typically the first solid introduced due to its high iron content. Cereals can be made of rice, barley, or oatmeal. Generally, salt, sugar, processed meat, juices, and canned foods should be avoided.

Though infants usually start eating solid foods between 4 and 6 months of age, more and more solid foods are consumed by a growing toddler. Pediatricians recommended introducing foods one at a time, and for a few days, in order to identify any potential food allergies. Toddlers may be picky at times, but it remains important to introduce a variety of foods and offer food with essential vitamins and nutrients, including iron, calcium, and vitamin D.


About 9 million children in the United States are malnourished (Children’s Welfare, 1998). More still suffer from milk anemia, a condition in which milk consumption leads to a lack of iron in the diet. The prevalence of iron deficiency anemia in 1- to 3-year-old children seems to be increasing (Kazal, 2002). The body gets iron through certain foods. Toddlers who drink too much cow’s milk may also become anemic if they are not eating other healthy foods that have iron. This can be due to the practice of giving toddlers milk as a pacifier when resting, riding, walking, and so on. Appetite declines somewhat during toddlerhood and a small amount of milk (especially with added chocolate syrup) can easily satisfy a child’s appetite for many hours. The calcium in milk interferes with the absorption of iron in the diet as well. There is also a link between iron deficiency anemia and diminished mental, motor, and behavioral development. In the second year of life, iron deficiency can be prevented by the use of a diversified diet that is rich in sources of iron and vitamin C, limiting cow’s milk consumption to less than 24 ounces per day, and providing a daily iron-fortified vitamin. 

Children in developing countries and countries experiencing the harsh conditions of war are at risk for two major types of malnutrition. Infantile marasmus refers to starvation due to a lack of calories and protein. Children who do not receive adequate nutrition lose fat and muscle until their bodies can no longer function. Babies who are breastfed are much less at risk of malnutrition than those who are bottle-fed. After weaning, children who have diets deficient in protein may experience kwashiorkor or the “disease of the displaced child,” often occurring after another child has been born and taken over breastfeeding. This results in a loss of appetite and swelling of the abdomen as the body begins to break down the vital organs as a source of protein


Link to Learning

The website Zero to Three has more information on infant sleep patterns and habits. Feel free to explore their multiple topics on the subject.


Preventing communicable diseases from early infancy is one of the major tasks of the Public Health System in the USA. Infants mouth every single object they find as one of their typical developmental tasks. They learn through their senses and tasting objects stimulates their brain and provides a sensory experience as well as learning.

Infants have much contact with dirty surfaces. They lay on a carpet that most likely has been contaminated by adults walking on it; they mouth keys, rattles, toys, and books; they crawl on the floor; they hold on to furniture to walk, and much more. How do we prevent infants from getting sick? One possible answer is immunizations.

Many decades ago, our society struggled to find vaccines and cures for illnesses such as Polio, whooping cough, and many other medical conditions. A few decades ago parents started changing their minds on the need to vaccinate children. Some children are not vaccinated for valid medical reasons, but some states allow a child to be unvaccinated because of a parent’s personal or religious beliefs. At least 1 in 14 children is not vaccinated. What is the outcome of not vaccinating children? Some of the preventable illnesses are returning. Fortunately, each vaccinated child stops the transmission of the disease, a phenomenon called herd immunity. Usually, if 90% of the people in a community (a herd) are immunized, no one dies of that disease.

In 2017, Community Care Licensing in California, the agency that regulates childcare centers, changed regulations. Before it was possible for parents to opt-out of vaccinations due to personal beliefs, but this changed after Governor Brown signed a Bill in 2016 to only exclude children from being vaccinated if there were medical reasons. Furthermore, all personnel working with children must be immunized.

Link to Learning

Read more information about vaccinations at the website Shots for School.

What you’ll learn to do: explain cognitive development in infants and toddlers

A toddler building a tower out of colorful blocks

In addition to rapid physical growth, young children also exhibit significant development of their cognitive abilities, particularly in language acquisition and in the ability to think and reason. You already learned a little bit about Piaget’s theory of cognitive development, and in this section, we’ll apply that model to cognitive tasks during infancy and toddlerhood. Piaget described intelligence in infancy as sensorimotor or based on direct, physical contact where infants use senses and motor skills to taste, feel, pound, push, hear, and move in order to experience the world. These basic motor and sensory abilities provide the foundation for the cognitive skills that will emerge during the subsequent stages of cognitive development.

Learning outcomes

  • Describe each of Piaget’s theories and stages of sensorimotor intelligence
  • Explain learning and memory abilities in infants and toddlers
  • Describe stages of language development during infancy
  • Compare theories of language development in toddlers
  • Explain the procedure, results, and implications of Hamlin and Wynn’s research on moral reasoning in infants

Cognitive Development

Cognitive Development in Children

In order to adapt to the evolving environment around us, humans rely on cognition, both adapting to the environment and also transforming it. In general, all theorists studying cognitive development address three main issues:

  1. The typical course of cognitive development
  2. The unique differences between individuals
  3. The mechanisms of cognitive development (the way genetics and environment combine to generate patterns of change)

The Cognitive Perspective: The Roots of Understanding

Cognitive theories focus on how our mental processes or cognitions change over time. The theory of cognitive development is a comprehensive theory about the nature and development of human intelligence first developed by Jean Piaget. It is primarily known as a developmental stage theory, but in fact, it deals with the nature of knowledge itself and how humans come gradually to acquire it, construct it, and use it. Moreover, Piaget claims that cognitive development is at the center of the human organism and language is contingent on cognitive development. Let’s learn more about Piaget’s views about the nature of intelligence and then dive deeper into the stages that he identified as critical in the developmental process.

Stages of Cognitive Development

Like Freud and Erikson, Piaget thought development unfolded in a series of stages approximately associated with age ranges. He proposed a theory of cognitive development that unfolds in four stages: sensorimotor, preoperational, concrete operational, and formal operational.

Table 1. Piaget’s Stages of Cognitive Development
Age (years) Stage Description Developmental issues
0–2 Sensorimotor World experienced through senses and actions Object permanence
Stranger anxiety
2–7 Preoperational Use words and images to represent things but lack logical reasoning Pretend play
Language development
7–11 Concrete operational Understand concrete events and logical analogies; perform arithmetical operations Conservation
Mathematical transformations
11– Formal operational Utilize abstract reasoning and hypothetical thinking Abstract logic
Moral reasoning

Piaget and Sensorimotor Intelligence

Adorable smiling toddler boy.
Figure 1. Toddlers happily explore the world, engaged in purposeful goal-directed behavior.

How do infants connect and make sense of what they are learning? Remember that Piaget believed that we are continuously trying to maintain cognitive equilibrium, or balance, between what we see and what we know (Piaget, 1954). Children have much more of a challenge in maintaining this balance because they are constantly being confronted with new situations, new words, new objects, etc. All this new information needs to be organized, and a framework for organizing information is referred to as a schema. Children develop schemas through the processes of assimilation and accommodation.

For example, 2-year-old Deja learned the schema for dogs because her family has a Poodle. When Deja sees other dogs in her picture books, she says, “Look mommy, dog!” Thus, she has assimilated them into her schema for dogs. One day, Deja sees a sheep for the first time and says, “Look mommy, dog!” Having a basic schema that a dog is an animal with four legs and fur, Deja thinks all furry, four-legged creatures are dogs. When Deja’s mom tells her that the animal she sees is a sheep, not a dog, Deja must accommodate her schema for dogs to include more information based on her new experiences. Deja’s schema for dog was too broad since not all furry, four-legged creatures are dogs. She now modifies her schema for dogs and forms a new one for sheep.

Let’s examine the transition that infants make from responding to the external world reflexively as newborns, to solving problems using mental strategies as two-year-olds. Piaget called this first stage of cognitive development sensorimotor intelligence (the sensorimotor period) because infants learn through their senses and motor skills. He subdivided this period into six substages:

Table 1. Sensorimotor substages.
Stage Age
Stage 1 – Reflexes Birth to 6 weeks
Stage 2 – Primary Circular Reactions 6 weeks to 4 months
Stage 3 – Secondary Circular Reactions 4 months to 8 months
Stage 4 – Coordination of Secondary Circular Reactions 8 months to 12 months
Stage 5 – Tertiary Circular Reactions 12 months to 18 months
Stage 6 – Mental Representation 18 months to 24 months

Substages of Sensorimotor Intelligence

For an overview of the substages of sensorimotor thought, it helps to group the six substages into pairs. The first two substages involve the infant’s responses to its own body, call primary circular reactions. During the first month first (substage one), the infant’s senses, as well as motor reflexes are the foundation of thought.

Substage One: Reflexive Action (Birth through 1st month)

This active learning begins with automatic movements or reflexes (sucking, grasping, staring, listening). A ball comes into contact with an infant’s cheek and is automatically sucked on and licked. But this is also what happens with a sour lemon, much to the infant’s surprise! The baby’s first challenge is to learn to adapt the sucking reflex to bottles or breasts, pacifiers or fingers, each acquiring specific types of tongue movements to latch, suck, breath, and repeat. This adaptation demonstrates that infants have begun to make sense of sensations. Eventually, the use of these reflexes becomes more deliberate and purposeful as they move onto substage two.

Substage Two: First Adaptations to the Environment (1st through 4th months)

Fortunately, within a few days or weeks, the infant begins to discriminate between objects and adjust responses accordingly as reflexes are replaced with voluntary movements. An infant may accidentally engage in a behavior and find it interesting, such as making a vocalization. This interest motivates trying to do it again and helps the infant learn a new behavior that originally occurred by chance. The behavior is identified as circular and primary because it centers on the infant’s own body. At first, most actions have to do with the body, but in months to come, will be directed more toward objects. For example, the infant may have different sucking motions for hunger and others for comfort (i.e. sucking a pacifier differently from a nipple or attempting to hold a bottle to suck it).

The next two substages (3 and 4), involve the infant’s responses to objects and people, called secondary circular reactions. Reactions are no longer confined to the infant’s body and are now interactions between the baby and something else.

Substage Three: Repetition (4th through 8th months)

During the next few months, the infant becomes more and more actively engaged in the outside world and takes delight in being able to make things happen by responding to people and objects. Babies try to continue any pleasing event. Repeated motion brings particular interest as the infant is able to bang two lids together or shake a rattle and laugh. Another example might be to clap their hands when a caregiver says “patty-cake.” Any sight of something delightful will trigger efforts for interaction.

Substage Four: New Adaptations and Goal-Directed Behavior (8th through 12th months)

Now the infant becomes more deliberate and purposeful in responding to people and objects and can engage in behaviors that others perform and anticipate upcoming events. Babies may ask for help by fussing, pointing, or reaching up to accomplish tasks, and work hard to get what they want. Perhaps because of continued maturation of the prefrontal cortex, the infant becomes capable of having a thought and carrying out a planned, goal-directed activity such as seeking a toy that has rolled under the couch or indicating that they are hungry. The infant is coordinating both internal and external activities to achieve a planned goal and begins to get a sense of social understanding. Piaget believed that at about 8 months (during substage 4), babies first understood the concept of object permanence, which is the realization that objects or people continue to exist when they are no longer in sight.

The last two stages (5 and 6), called tertiary circular reactions, consist of actions (stage 5) and ideas (stage 6) where infants become more creative in their thinking.

Substage Five: Active Experimentation of “Little Scientists” (12th through 18th months)

The toddler is considered a “little scientist” and begins exploring the world in a trial-and-error manner, using motor skills and planning abilities. For example, the child might throw their ball down the stairs to see what happens or delight in squeezing all of the toothpaste out of the tube. The toddler’s active engagement in experimentation helps them learn about their world. Gravity is learned by pouring water from a cup or pushing bowls from high chairs. The caregiver tries to help the child by picking it up again and placing it on the tray. And what happens? Another experiment! The child pushes it off the tray again causing it to fall and the caregiver to pick it up again! A closer examination of this stage causes us to really appreciate how much learning is going on at this time and how many things we come to take for granted must actually be learned. This is a wonderful and messy time of experimentation and most learning occurs by trial and error.

Substage Six: Mental Representations (18th month to 2 years of age)

The child is now able to solve problems using mental strategies, to remember something heard days before and repeat it, to engage in pretend play, and to find objects that have been moved even when out of sight. Take, for instance, the child who is upstairs in a room with the door closed, supposedly taking a nap. The doorknob has a safety device on it that makes it impossible for the child to turn the knob. After trying several times to push the door or turn the doorknob, the child carries out a mental strategy to get the door opened – he knocks on the door! Obviously, this is a technique learned from the past experience of hearing a knock on the door and observing someone opening the door. The child is now better equipped with mental strategies for problem-solving. Part of this stage also involves learning to use language. This initial movement from the “hands-on” approach to knowing about the world to the more mental world of stage six marked the transition to preoperational thinking, which you’ll learn more about in a later module.

Development of Object Permanence

A critical milestone during the sensorimotor period is the development of object permanence. Introduced during substage 4 above, object permanence is the understanding that even if something is out of sight, it continues to exist. The infant is now capable of making attempts to retrieve the object. Piaget thought that, at about 8 months, babies first understand the concept of objective permanence, but some research has suggested that infants seem to be able to recognize that objects have permanence at much younger ages (even as young as 4 months of age). Other researchers, however, are not convinced (Mareschal & Kaufman, 2012). It may be a matter of “grasping vs. mastering” the concept of objective permanence. Overall, we can expect children to grasp the concept that objects continue to exist even when they are not in sight by around 8 months old, but memory may play a factor in their consistency. Because toddlers (i.e., 12–24 months old) have mastered object permanence, they enjoy games like hide-and-seek, and they realize that when someone leaves the room they will come back (Loop, 2013). Toddlers also point to pictures in books and look in the appropriate places when you ask them to find objects.

Learning and Memory Abilities in Infants

Memory is central to cognitive development. Our memories form the basis for our sense of self, guide our thoughts and decisions, influence our emotional reactions, and allow us to learn (Bauer, 2008).

It is thought that Piaget underestimated memory ability in infants (Schneider, 2015). This belief came in part from findings that adults rarely recall personal events from before the age of 3 years (a phenomenon that is known as infantile or childhood amnesia). However, research with infants and young children has made it clear that they can and do form memories of events. 

As mentioned when discussing the development of infant senses, within the first few weeks of birth, infants recognize their caregivers by face, voice, and smell. Sensory and caregiver memories are apparent in the first month, motor memories by 3 months, and then, at about 9 months, more complex memories including language (Mullally & Maguire, 2014). There is an agreement that memory is fragile in the first months of life, but that improves with age. Repeated sensations and brain maturation are required in order to process and recall events (Bauer, 2008). Infants remember things that happened weeks and months ago (Mullally & Maguire, 2014), although they most likely will not remember it decades later. From the cognitive perspective, this has been explained by the idea that the lack of linguistic skills of babies and toddlers limit their ability to mentally represent events; thereby, reducing their ability to encode memory. Moreover, even if infants do form such early memories, older children and adults may not be able to access them because they may be employing very different, more linguistically based, retrieval cues than infants used when forming the memory. 

Language Development

Given the remarkable complexity of a language, one might expect that mastering a language would be an especially arduous task; indeed, for those of us trying to learn a second language as adults, this might seem to be true. However, young children master language very quickly with relative ease. B. F. Skinner (1957) proposed that language is learned through reinforcement. Noam Chomsky (1965) criticized this behaviorist approach, asserting instead that the mechanisms underlying language acquisition are biologically determined. The use of language develops in the absence of formal instruction and appears to follow a very similar pattern in children from vastly different cultures and backgrounds. It would seem, therefore, that we are born with a biological predisposition to acquire a language (Chomsky, 1965; Fernández & Cairns, 2011). Moreover, it appears that there is a critical period for language acquisition, such that this proficiency at acquiring language is maximal early in life; generally, as people age, the ease with which they acquire and master new languages diminishes (Johnson & Newport, 1989; Lenneberg, 1967; Singleton, 1995).

Children begin to learn about language from a very early age (Table 1). In fact, it appears that this is occurring even before we are born. Newborns show a preference for their mother’s voice and appear to be able to discriminate between the language spoken by their mother and other languages. Babies are also attuned to the languages being used around them and show preferences for videos of faces that are moving in synchrony with the audio of spoken language versus videos that do not synchronize with the audio (Blossom & Morgan, 2006; Pickens, 1994; Spelke & Cortelyou, 1981).

Table 2. Stages of Language and Communication Development
Stage Age Developmental Language and Communication
1 0–3 months Reflexive communication
2 3–8 months Reflexive communication; interest in others
3 8–12 months Intentional communication; sociability
4 12–18 months First words
5 18–24 months Simple sentences of two words
6 2–3 years Sentences of three or more words
7 3–5 years Complex sentences; has conversations

Each language has its own set of phonemes that are used to generate morphemes, words, and so on. Babies can discriminate among the sounds that make up a language (for example, they can tell the difference between the “s” in vision and the “ss” in fission); early on, they can differentiate between the sounds of all human languages, even those that do not occur in the languages that are used in their environments. However, by the time that they are about 1 year old, they can only discriminate among those phonemes that are used in the language or languages in their environments (Jensen, 2011; Werker & Lalonde, 1988; Werker & Tees, 1984).


The achievement gap refers to the persistent difference in grades, test scores, and graduation rates that exist among students of different ethnicities, races, and—in certain subjects—sexes (Winerman, 2011). Research suggests that these achievement gaps are strongly influenced by differences in socioeconomic factors that exist among the families of these children. While the researchers acknowledge that programs aimed at reducing such socioeconomic discrepancies would likely aid in equalizing the aptitude and performance of children from different backgrounds, they recognize that such large-scale interventions would be difficult to achieve. Therefore, it is recommended that programs aimed at fostering aptitude and achievement among disadvantaged children may be the best option for dealing with issues related to academic achievement gaps (Duncan & Magnuson, 2005).

Low-income children perform significantly more poorly than their middle- and high-income peers on a number of educational variables: They have significantly lower standardized test scores, graduation rates, and college entrance rates, and they have much higher school dropout rates. There have been attempts to correct the achievement gap through state and federal legislation, but what if the problems start before the children even enter school?

Psychologists Betty Hart and Todd Risley (2006) spent their careers looking at the early language ability and progression of children in various income levels. In one longitudinal study, they found that although all the parents in the study engaged and interacted with their children, middle- and high-income parents interacted with their children differently than low-income parents. After analyzing 1,300 hours of parent-child interactions, the researchers found that middle- and high-income parents talk to their children significantly more, starting when the children are infants. By 3 years old, high-income children knew almost double the number of words known by their low-income counterparts, and they had heard an estimated total of 30 million more words than the low-income counterparts (Hart & Risley, 2003). And the gaps only become more pronounced. Before entering kindergarten, high-income children score 60% higher on achievement tests than their low-income peers (Lee & Burkam, 2002).

There are solutions to this problem. At the University of Chicago, experts are working with low-income families, visiting them at their homes, and encouraging them to speak more to their children on a daily and hourly basis. Other experts are designing preschools in which students from diverse economic backgrounds are placed in the same classroom. In this research, low-income children made significant gains in their language development, likely as a result of attending the specialized preschool (Schechter & Byeb, 2007). What other methods or interventions could be used to decrease the achievement gap? What types of activities could be implemented to help the children of your community or a neighboring community?

Infant Communication

Wide-eyed baby boy.
Figure 2. Before they develop language, infants communicate using facial expressions.

Intentional Vocalizations

Infants begin to vocalize and repeat vocalizations within the first couple of months of life. That gurgling, musical vocalization called cooing can serve as a source of entertainment to an infant who has been laid down for a nap or seated in a carrier on a car ride. Cooing serves as practice for vocalization. It also allows the infant to hear the sound of their own voice and try to repeat sounds that are entertaining. Infants also begin to learn the pace and pause of conversation as they alternate their vocalization with that of someone else and then take their turn again when the other person’s vocalization has stopped. Cooing initially involves making vowel sounds like “oooo.” Later, as the baby moves into babbling (see below), consonants are added to vocalizations such as “nananananana.”

Babbling and Gesturing

Between 6 and 9 months, infants begin making even more elaborate vocalizations that include the sounds required for any language. Guttural sounds, clicks, consonants, and vowel sounds stand ready to equip the child with the ability to repeat whatever sounds are characteristic of the language heard. These babies repeat certain syllables (ma-ma-ma, da-da-da, ba-ba-ba), a vocalization called babbling because of the way it sounds. Eventually, these sounds will no longer be used as the infant grows more accustomed to a particular language. Deaf babies also use gestures to communicate wants, reactions, and feelings. Because gesturing seems to be easier than vocalization for some toddlers, sign language is sometimes taught to enhance one’s ability to communicate by making use of the ease of gesturing. The rhythm and pattern of language are used when deaf babies sign just as when hearing babies babble.

At around ten months of age, infants can understand more than they can say. You may have experienced this phenomenon as well if you have ever tried to learn a second language. You may have been able to follow a conversation more easily than to contribute to it.

Holophrastic Speech

Children begin using their first words at about 12 or 13 months of age and may use partial words to convey thoughts at even younger ages. These one-word expressions are referred to as holophrastic speech (holophrase). For example, the child may say “ju” for the word “juice” and use this sound when referring to a bottle. The listener must interpret the meaning of the holophrase. When this is someone who has spent time with the child, interpretation is not too difficult. They know that “ju” means “juice” which means the baby wants some milk! But, someone who has not been around the child will have trouble knowing what is meant. Imagine the parent who exclaims to a friend, “Ezra’s talking all the time now!” The friend hears only “ju da ga” which, the parent explains, means “I want some milk when I go with Daddy.”


A child who learns that a word stands for an object may initially think that the word can be used for only that particular object. Only the family’s Irish Setter is a “doggie.” This is referred to as underextension. More often, however, a child may think that a label applies to all objects that are similar to the original object. In overextension, all animals become “doggies,” for example.

First words and cultural influences

The first words for English-speaking children tend to be nouns. The child labels objects such as a cup or a ball. In a verb-friendly language such as Chinese, however, children may learn more verbs. This may also be due to the different emphasis given to objects based on culture. Chinese children may be taught to notice action and relationships between objects while children from the United States may be taught to name an object and its qualities (color, texture, size, etc.). These differences can be seen when comparing interpretations of art by older students from China and the United States.

Vocabulary growth spurt

One-year-olds typically have a vocabulary of about 50 words. But by the time they become toddlers, they have a vocabulary of about 200 words and begin putting those words together in telegraphic speech (short phrases). This language growth spurt is called the naming explosion because many early words are nouns (persons, places, or things).

Two-word sentences and telegraphic speech

Words are soon combined and 18-month-old toddlers can express themselves further by using phrases such as “baby bye-bye” or “doggie pretty.” Words needed to convey messages are used, but the articles and other parts of speech necessary for grammatical correctness are not yet included. These expressions sound like a telegraph (or perhaps a better analogy today would be that they read like a text message) where unnecessary words are not used. “Give baby ball” is used rather than “Give the baby the ball.” Or a text message of “Send money now!” rather than “Dear Mother. I really need some money to take care of my expenses.” You get the idea.

Child-directed speech

Why is a horse a “horsie”? Have you ever wondered why adults tend to use “baby talk” or that sing-song type of intonation and exaggeration used when talking to children? This represents a universal tendency and is known as child-directed speech or motherese or parentese. It involves exaggerating the vowel and consonant sounds, using a high-pitched voice, and delivering the phrase with great facial expression. Why is this done? It may be in order to clearly articulate the sounds of a word so that the child can hear the sounds involved. Or it may be because when this type of speech is used, the infant pays more attention to the speaker and this sets up a pattern of interaction in which the speaker and listener are in tune with one another. When I demonstrate this in class, the students certainly pay attention and look my way. Amazing! It also works in the college classroom!

Theories of Language Development

How is language learned? Each major theory of language development emphasizes different aspects of language learning: that infants’ brains are genetically attuned to language, that infants must be taught and that infants’ social impulses foster language learning. The first two theories of language development represent two extremes in the level of interaction required for language to occur (Berk, 2007).

Chomsky and the language acquisition device

This theory posits that infants teach themselves and that language learning is genetically programmed. The view is known as nativism and was advocated by Noam Chomsky, who suggested that infants are equipped with a neurological construct referred to as the language acquisition device (LAD), which makes infants ready for language. The LAD allows children, as their brains develop, to derive the rules of grammar quickly and effectively from the speech they hear every day. Therefore, language develops as long as the infant is exposed to it. No teaching, training, or reinforcement is required for language to develop. Instead, language learning comes from a particular gene, brain maturation, and the overall human impulse to imitate.

Skinner and reinforcement

This theory is the opposite of Chomsky’s theory because it suggests that infants need to be taught language. This idea arises from behaviorism. Learning theorist, B. F. Skinner, suggested that language develops through the use of reinforcement. Sounds, words, gestures, and phrases are encouraged by following the behavior with attention, words of praise, treats, or anything that increases the likelihood that the behavior will be repeated. This repetition strengthens associations, so infants learn the language faster as parents speak to them often. For example, when a baby says “ma-ma,” the mother smiles and repeats the sound while showing the baby attention. So, “ma-ma” is repeated due to this reinforcement.

Social pragmatics

Another language theory emphasizes the child’s active engagement in learning the language out of a need to communicate. Social impulses foster infant language because humans are social beings and we must communicate because we are dependent on each other for survival. The child seeks information, memorizes terms, imitates the speech heard from others and learns to conceptualize using words as language is acquired. Tomasello &  Herrmann (2010) argue that all human infants, as opposed to chimpanzees, seek to master words and grammar in order to join the social world. Many would argue that all three of these theories (Chomsky’s argument for nativism, conditioning, and social pragmatics) are important for fostering the acquisition of language (Berger, 2004).

Moral Reasoning in Infants

The Foundation of Moral Reasoning in Infants

Young baby, around 6 months old, doing tummy time and looking happily at the camera.
Figure 3. Maybe babies know more than we think they do!

The work of Lawrence Kohlberg was an important start to modern research on moral development and reasoning. However, Kohlberg relied on a specific method: he presented moral dilemmas and asked children and adults to explain what they would do and—more importantly—why they would act in that particular way. Kohlberg found that children tended to make choices based on avoiding punishment and gaining praise. But children are at a disadvantage compared to adults when they must rely on language to convey their inner thoughts and emotional reactions, so what they say may not adequately capture the complexity of their thinking.

Starting in the 1980s, developmental psychologists created new methods for studying the thought processes of children and infants long before they acquire language. One particularly effective method is to present children with puppet shows to grab their attention and then record nonverbal behaviors, such as looking and choosing, to identify children’s preferences or interests.

A research group at Yale University has been using the puppet show technique to study the moral thinking of children for much of the past decade. What they have discovered has given us a glimpse of surprisingly complex thought processes that may serve as the foundation of moral reasoning.

Remember that Lawrence Kohlberg thought that children at this age—and, in fact, through 9 years of age—are primarily motivated to avoid punishment and seek rewards. Neither Kohlberg nor Carol Gilligan nor Jean Piaget was likely to predict that infants would develop preferences based on the type of behavior shown by other individuals.

What you’ll learn to do: explain emotional and social development during infancy

Two infants lying on their stomachs looking at each other

Psychosocial development occurs as children form relationships, interact with others, and understand and manage their feelings. In emotional and social development, forming healthy attachments is very important and is the major social milestone of infancy. Attachment is a long-standing connection or bond with others. Developmental psychologists are interested in how infants reach this milestone. They ask questions such as: how do parent and infant attachment bonds form? How does neglect affect these bonds? What accounts for children’s attachment differences?

Learning outcomes

  • Describe emotional development and self-awareness during infancy
  • Contrast styles of attachment
  • Use Erikson’s theory to characterize psychosocial development during infancy

Emotional Development and Attachment

Emotional Development

At birth, infants exhibit two emotional responses: attraction and withdrawal. They show attraction to pleasant situations that bring comfort, stimulation, and pleasure. And they withdraw from unpleasant stimulation such as bitter flavors or physical discomfort. At around two months, infants exhibit social engagement in the form of social smiling as they respond with smiles to those who engage their positive attention. Pleasure is expressed as laughter at 3 to 5 months of age, and displeasure becomes more specific to fear, sadness, or anger (usually triggered by frustration) between ages 6 and 8 months. Where anger is a healthy response to frustration, sadness, which appears in the first months as well, usually indicates withdrawal (Thiam et al., 2017).

As reviewed above, infants progress from reactive pain and pleasure to complex patterns of socioemotional awareness, which is a transition from basic instincts to learned responses. Fear is not always focused on things and events; it can also involve social responses and relationships. The fear is often associated with the presence of strangers or the departure of significant others known respectively as stranger wariness and separation anxiety, which appear sometime between 6 and 15 months. And there is even some indication that infants may experience jealousy as young as 6 months of age (Hart & Carrington, 2002).

Stranger wariness actually indicates that brain development and increased cognitive abilities have taken place. As an infant’s memory develops, they are able to separate the people that they know from the people that they do not. The same cognitive advances allow infants to respond positively to familiar people and recognize those that are not familiar. Separation anxiety also indicates cognitive advances and is universal across cultures. Due to the infant’s increased cognitive skills, they are able to ask reasonable questions like “Where is my caregiver going?” “Why are they leaving?” or “Will they come back?” Separation anxiety usually begins around 7-8 months and peaks around 14 months, and then decreases. Both stranger wariness and separation anxiety represent important social progress because they not only reflect cognitive advances but also growing social and emotional bonds between infants and their caregivers.

As we will learn through the rest of this module, caregiving does matter in terms of infant emotional development and emotional regulation. Emotional regulation can be defined by two components: emotions as regulating and emotions as regulated. The first, “emotions as regulating,” refers to changes that are elicited by activated emotions (e.g., a child’s sadness eliciting a change in parent response). The second component is labeled “emotions as regulated,” which refers to the process through which the activated emotion is itself changed by deliberate actions taken by the self (e.g., self-soothing, distraction) or others (e.g., comfort).

Throughout infancy, children rely heavily on their caregivers for emotional regulation; this reliance is labeled co-regulation, as parents and children both modify their reactions to the other based on the cues from the other. Caregivers use strategies such as distraction and sensory input (e.g., rocking, stroking) to regulate infants’ emotions. Despite their reliance on caregivers to change the intensity, duration, and frequency of emotions, infants are capable of engaging in self-regulation strategies as young as 4 months old. At this age, infants intentionally avert their gaze from overstimulating stimuli. By 12 months, infants use their mobility in walking and crawling to intentionally approach or withdraw from stimuli.

Throughout toddlerhood, caregivers remain important for the emotional development and socialization of their children, through behaviors such as labeling their child’s emotions, prompting thought about emotion (e.g., “why is the turtle sad?”), continuing to provide alternative activities/distractions, suggesting coping strategies, and modeling coping strategies. Caregivers who use such strategies and respond sensitively to children’s emotions tend to have children who are more effective at emotion regulation, are less fearful and fussy, more likely to express positive emotions, easier to soothe, more engaged in environmental exploration, and have enhanced social skills in the toddler and preschool years.


During the second year of life, children begin to recognize themselves as they gain a sense of the self as an object. The realization that one’s body, mind, and activities are distinct from those of other people is known as self-awareness (Kopp, 2011). The most common technique used in research for testing self-awareness in infants is a mirror test known as the “Rouge Test.” The rouge test works by applying a dot of rouge (colored makeup) on an infant’s face and then placing them in front of the mirror. If the infant investigates the dot on their nose by touching it, they are thought to realize their own existence and have achieved self-awareness. A number of research studies have used this technique and shown self-awareness to develop between 15 and 24 months of age. Some researchers also take language such as “I, me, my, etc.” as an indicator of self-awareness.

Cognitive psychologist Philippe Rochat (2003) described a more in-depth developmental path in acquiring self-awareness through various stages. He described self-awareness as occurring in five stages beginning from birth.

Table 1. Stages of acquiring self-awareness
Stage Description
Stage 1 – Differentiation (from birth) Right from birth infants are able to differentiate the self from the non-self. A study using the infant rooting reflex found that infants rooted significantly less from self-stimulation, contrary to when the stimulation came from the experimenter.
Stage 2 – Situation (by 2 months) In addition to differentiation, infants at this stage can also situate themselves in relation to a model. In one experiment infants were able to imitate tongue orientation from an adult model. Additionally, another sign of differentiation is when infants bring themselves into contact with objects by reaching for them.
Stage 3 – Identification (by 2 years) At this stage, the more common definition of “self-awareness” comes into play, where infants can identify themselves in a mirror through the “rouge test” as well as begin to use language to refer to themselves.
Stage 4 – Permanence This stage occurs after infancy when children are aware that their sense of self continues to exist across both time and space.
Stage 5 – Self-consciousness or meta-self-awareness This also occurs after infancy. This is the final stage when children can see themselves in 3rd person, or how they are perceived by others.

Once a child has achieved self-awareness, the child is moving toward understanding social emotions such as guilt, shame or embarrassment, and pride, as well as sympathy and empathy. These will require an understanding of the mental state of others which is acquired around age 3 to 5 and will be explored in the next module (Berk, 2007).


Psychosocial development occurs as children form relationships, interact with others, and understand and manage their feelings. In social and emotional development, forming healthy attachments is very important and is the major social milestone of infancy. Attachment is a long-standing connection or bond with others. Developmental psychologists are interested in how infants reach this milestone. They ask questions such as: How do parent and infant attachment bonds form? How does neglect affect these bonds? What accounts for children’s attachment differences?

Researchers Harry Harlow, John Bowlby, and Mary Ainsworth conducted studies designed to answer these questions. In the 1950s, Harlow conducted a series of experiments on monkeys. He separated newborn monkeys from their mothers. Each monkey was presented with two surrogate mothers. One surrogate mother was made out of wire mesh, and she could dispense milk. The other surrogate mother was softer and made from cloth: This monkey did not dispense milk. Research shows that the monkeys preferred the soft, cuddly cloth monkey, even though she did not provide any nourishment. The baby monkeys spent their time clinging to the cloth monkey and only went to the wire monkey when they needed to be feed. Prior to this study, the medical and scientific communities generally thought that babies become attached to the people who provide their nourishment. However, Harlow (1958) concluded that there was more to the mother-child bond than nourishment. Feelings of comfort and security are the critical components of maternal-infant bonding, which leads to healthy psychosocial development.

Building on the work of Harlow and others, John Bowlby developed the concept of attachment theory. He defined attachment as the affectional bond or tie that an infant forms with the mother (Bowlby, 1969). He believed that an infant must form this bond with a primary caregiver in order to have normal social and emotional development. In addition, Bowlby proposed that this attachment bond is very powerful and continues throughout life. He used the concept of a secure base to define a healthy attachment between parent and child (1988). A secure base is a parental presence that gives children a sense of safety as they explore their surroundings. Bowlby said that two things are needed for a healthy attachment: The caregiver must be responsive to the child’s physical, social, and emotional needs; and the caregiver and child must engage in mutually enjoyable interactions (Bowlby, 1969).

A person is shown holding an infant.
Figure 1. Mutually enjoyable interactions promote the mother-infant bond. (credit: Peter Shanks)

While Bowlby thought attachment was an all-or-nothing process, Mary Ainsworth’s (1970) research showed otherwise. Ainsworth wanted to know if children differ in the ways they bond, and if so, how. To find the answers, she used the Strange Situation procedure to study attachment between mothers and their infants (1970). In the Strange Situation, the mother (or primary caregiver) and the infant (age 12-18 months) are placed in a room together.  There are toys in the room, and the caregiver and child spend some time alone in the room. After the child has had time to explore their surroundings, a stranger enters the room. The mother then leaves her baby with the stranger. After a few minutes, she returns to comfort her child.

Based on how the toddlers responded to the separation and reunion, Ainsworth identified three types of parent-child attachments: secure, avoidant, and resistant (Ainsworth & Bell, 1970). A fourth style, known as disorganized attachment, was later described (Main & Solomon, 1990).

The most common type of attachment—also considered the healthiest—is called secure attachment. In this type of attachment, the toddler prefers their parent over a stranger. The attachment figure is used as a secure base to explore the environment and is sought out in times of stress. Securely attached children were distressed when their caregivers left the room in the Strange Situation experiment, but when their caregivers returned, the securely attached children were happy to see them. Securely attached children have caregivers who are sensitive and responsive to their needs.

A photograph shows a person squatting down next to a small child who is standing up.
Figure 2. In a secure attachment, the parent provides a secure base for the toddler, allowing him to securely explore his environment. (credit: Kerry Ceszyk)

With avoidant attachment, the child is unresponsive to the parent, does not use the parent as a secure base, and does not care if the parent leaves. The toddler reacts to the parent the same way they react to a stranger. When the parent does return, the child is slow to show a positive reaction. Ainsworth theorized that these children were most likely to have a caregiver who was insensitive and inattentive to their needs (Ainsworth, Blehar, Waters, & Wall, 1978).

In cases of resistant attachment, children tend to show clingy behavior, but then they reject the attachment figure’s attempts to interact with them (Ainsworth & Bell, 1970). These children do not explore the toys in the room, appearing too fearful. During separation in the Strange Situation, they become extremely disturbed and angry with the parent. When the parent returns, the children are difficult to comfort. Resistant attachment is thought to be the result of the caregivers’ inconsistent level of response to their child.

Finally, children with disorganized attachment behaved oddly in the Strange Situation. They freeze, run around the room in an erratic manner, or try to run away when the caregiver returns (Main & Solomon, 1990). This type of attachment is seen most often in kids who have been abused or severely neglected. Research has shown that abuse disrupts a child’s ability to regulate their emotions.

While Ainsworth’s research has found support in subsequent studies, it has also met criticism. Some researchers have pointed out that a child’s temperament (which we discuss next) may have a strong influence on attachment (Gervai, 2009; Harris, 2009), and others have noted that attachment varies from culture to culture, a factor that was not accounted for in Ainsworth’s research (Rothbaum, Weisz, Pott, Miyake, & Morelli, 2000; van Ijzendoorn & Sagi-Schwartz, 2008).

Attachment styles vary in the amount of security and closeness felt in the relationship and they can change with new experiences. The type of attachment fostered in parenting styles varies by culture as well. For example, German parents value independence and Japanese mothers are typically by their children’s sides. As a result, the rate of insecure-avoidant attachments is higher in Germany and insecure-resistant attachments are higher in Japan. These differences reflect cultural variation rather than true insecurity, however (van Ijzendoorn and Sagi, 1999).  Keep in mind that methods for measuring attachment styles have been based on a model that reflects middle-class, US values and interpretation. Newer methods for assessing attachment styles involve using a Q-sort technique in which a large number of behaviors are recorded on cards and the observer sorts the cards in a way that reflects the type of behavior that occurs within the situation.

Attachment is classified into four types: A, B, C, and D. Ainsworth’s original schema differentiated only three types of attachment (types A, B, and C), but, as mentioned above, later researchers discovered a fourth category (type D). As we explore styles of attachment below, consider how these may also be evidenced in adult relationships. We’ll come back to this idea in later modules.

Types of Attachments


A secure attachment (type B) is one in which the child feels confident that their needs will be met in a timely and consistent way. The caregiver is the base for exploration, providing assurance, and enabling discovery. In North America, this interaction may include an emotional connection in addition to adequate care. However, even in cultures where mothers do not talk, cuddle, and play with their infants, secure attachments can develop (LeVine et. al., 1994). Secure attachments can form provided the child has consistent contact and care from one or more caregivers. Consistency of contacts may be jeopardized if the infant is cared for in a daycare with a high turn-over of caregivers or if institutionalized and given little more than basic physical care. And while infants who, perhaps because of being in orphanages with inadequate care, have not had the opportunity to attach in infancy can form initial secure attachments several years later, they may have more emotional problems of depression or anger, or be overly friendly as they make adjustments (O’Connor et. al., 2003).

Insecure Resistant/Ambivalent

Insecure-resistant/ambivalent (type C) attachment style is marked by insecurity and resistance to engaging in activities or play away from the caregiver. It is as if the child fears that the caregiver will abandon them and clings accordingly. (Keep in mind that clingy behavior can also just be part of a child’s natural disposition or temperament and does not necessarily reflect some kind of parental neglect.) The child may cry if separated from the caregiver and also cry upon their return. They seek constant reassurance that never seems to satisfy their doubt. This type of insecure attachment might be a result of not having their needs met in a consistent or timely way. Consequently, the infant is never sure that the world is a trustworthy place or that he or she can rely on others without some anxiety. A caregiver who is unavailable, perhaps because of marital tension, substance abuse, or preoccupation with work, may send a message to the infant they cannot rely on having their needs met. A caregiver who attends to a child’s frustration can help teach them to be calm and to relax. But an infant who receives only sporadic attention when experiencing discomfort may not learn how to calm down.


Insecure-avoidant (type A) is an attachment style marked by insecurity. This style is also characterized by a tendency to avoid contact with the caregiver and with others. This child may have learned that needs typically go unmet and learns that the caregiver does not provide care and cannot be relied upon for comfort, even sporadically. An insecure-avoidant child learns to be more independent and disengaged. Such a child might sit passively in a room filled with toys until it is time to go.


Disorganized attachment (type D) represents the most insecure style of attachment and occurs when the child is given mixed, confused, and inappropriate responses from the caregiver. For example, a mother who suffers from schizophrenia may laugh when a child is hurting or cry when a child exhibits joy. The child does not learn how to interpret emotions or to connect with the unpredictable caregiver.

How common are the attachment styles among children in the United States? It is estimated that about 65 percent of children in the United States are securely attached. Twenty percent exhibit avoidant styles and 10 to 15 percent are resistant. Another 5 to 10 percent may be characterized as disorganized.

Erikson’s Stages for Infants and Toddlers

Erikson’s Psychosocial Stages of Development
Stage Age (years) Developmental Task Description
1 0–1 Trust vs. mistrust Trust (or mistrust) that basic needs, such as nourishment and affection, will be met
2 1–3 Autonomy vs. shame/doubt Develop a sense of independence in many tasks
3 3–6 Initiative vs. guilt Take initiative on some activities—may develop guilt when unsuccessful or boundaries overstepped
4 7–11 Industry vs. inferiority Develop self-confidence in abilities when competent or sense of inferiority when not
5 12–18 Identity vs. confusion Experiment with and develop identity and roles
6 19–29 Intimacy vs. isolation Establish intimacy and relationships with others
7 30–64 Generativity vs. stagnation Contribute to society and be part of a family
8 65– Integrity vs. despair Assess and make sense of life and meaning of contributions


messy toddler girl covered with fingerpaint.
Figure 4. Exploring the environment allows the toddler to develop a sense of autonomy and independence

Autonomy vs. shame and doubt (Will)

Autonomy vs. Shame (Will)—As toddlers (ages 1–3 years) begin to explore their world, they learn that they can control their actions and act on their environment to get results. They begin to show clear preferences for certain elements of the environment, such as food, toys, and clothing. A toddler’s main task is to resolve the issue of autonomy vs. shame and doubt by working to establish independence. This is the “me do it” stage. For example, we might observe a budding sense of autonomy in a 2-year-old child who wants to choose her clothes and dress herself. Although her outfits might not be appropriate for the situation, her input in such basic decisions has an effect on her sense of independence. If denied the opportunity to act on her environment, she may begin to doubt her abilities, which could lead to low self-esteem and feelings of shame.

As the child begins to walk and talk, an interest in independence or autonomy replaces their concern for trust. The toddler tests the limits of what can be touched, said, and explored. Erikson believed that toddlers should be allowed to explore their environment as freely as safety allows and, in doing so, will develop a sense of independence that will later grow to self-esteem, initiative, and overall confidence. If a caregiver is overly anxious about the toddler’s actions for fear that the child will get hurt or violate others’ expectations, the caregiver can give the child the message that they should be ashamed of their behavior and instill a sense of doubt in their abilities. Parenting advice based on these ideas would be to keep your toddler safe, but let them learn by doing. A sense of pride seems to rely on doing rather than being told how capable one is (Berger, 2005).



Theory of Psychosexual Development

Table 1. Freud’s Stages of Psychosexual Development
Stage Age (years) Erogenous Zone Major Conflict Adult Fixation Example
Oral 0–1 Mouth Weaning off breast or bottle Smoking, overeating
Anal 1–3 Anus Toilet training Neatness, messiness
Phallic 3–6 Genitals Oedipus/Electra complex Vanity, overambition
Latency 6–12 None None None
Genital 12+ Genitals None None

During the anal stage, which coincides with toddlerhood and potty-training, the child is taught that some urges must be contained and some actions postponed. There are rules about certain functions and when and where they are to be carried out. The child is learning a sense of self-control. The ego is being developed. If the caregiver is extremely controlling about potty training (stands over the child waiting for the smallest indication that the child might need to go to the potty and immediately scoops the child up and places him on the potty chair, for example), the child may grow up fearing losing control. He may become fixated in this stage or “anally retentive”—fearful of letting go. Such a person might be extremely neat and clean, organized, reliable, and controlling of others. If the caregiver neglects to teach the child to control urges, he may grow up to be “anal expulsive” or an adult who is messy, irresponsible, and disorganized.

Link to Learning: Toilet Training

To the relief of most parents, there is very little evidence to suggest that Freud was right about fixations caused during the anal stage, mainly because the theory itself would be very difficult to test. Nevertheless, parents worry about toilet training, and whether they will be able to guide their children through the process unscathed. has a good web page on to potty training that may help parents worried about toilet training.


A woman shown from behind walking and carrying an infant

We have explored the dramatic story of the first two years of life. Rapid physical growth, neurological development, language acquisition, the movement from hands-on to mental learning, an expanding emotional repertoire, and the initial conceptions of self and others make this period of life very exciting. These abilities are shaped into more sophisticated mental processes, self-concepts, and social relationships during the years of early childhood.

Babies begin to learn about the world around them from a very early age. Children’s early experiences, meaning the bonds they form with their parents and their first learning experiences, affect their future physical, cognitive, emotional, and social development. Various organizations and agencies are dedicated to helping parents (and other caregivers), educators, and health care providers understand the importance of early healthy development. Healthy development means that children of all abilities, including those with special health care needs, are able to grow up where their social, emotional, and educational needs are met. Having a safe and loving home and spending time with family―playing, singing, reading, and talking―are very important. Proper nutrition, exercise, and sleep can also make a big difference; and effective parenting practices are key to supporting healthy development (CDC, 2019). The need to invest in very young children is important to maximize their future well-being.

Additional Supplemental Resources


  • Areas and Function of the Brain
    • Students will interact with the map and chart to review major areas of the brain and their functions. Toggle down on the top left menu to choose different structures to explore.
  • CDC’s Information for Parents of Infants and Toddlers
    • Besides tracking your child’s growth and development, you can learn about topics such as developmental disabilities, immunization recommendations, and screening.
  • Infant and Toddler Nutrition
    • This website brings together existing information and practical strategies on feeding healthy foods and drinks to infants and toddlers, from birth to 24 months of age.
  • Zero to Three Healthy Sleep
    • The website information on infant sleep patterns and habits. Feel free to explore their multiple topics on the subject.
  • Institute for Learning and Brain Sciences
    • The Institute for Learning & Brain Sciences (I-LABS) is the world’s leading interdisciplinary research center on early learning and brain development.
      Our groundbreaking research is revolutionizing our understanding of children’s development in their early years, and revealing how this affects brain changes in adolescence, adulthood, and aging.


  • Working with children to understand how brains develop
    • See how developmental psychologists conduct research with young infants. Closed captioning available.
  • How Baby Brains Develop
    • CNN takes a look inside what might be the most complex biological system in the world: the human brain.
  • Harry Harlow’s Study of Attachment in Monkeys
    • This video shows that infant rhesus monkeys appear to form an affectional bond with soft, cloth surrogate mothers that offered no food but not with wire surrogate mothers that provided a food source but are less pleasant to touch.
  • The Strange Situation
    • This video shows the test that American psychologist Mary Ainsworth developed for studying attachment in infants.
  • The Attachment Theory: How Childhood Affects Life
    • The attachment theory argues that a strong emotional and physical bond to one primary caregiver in our first years of life is critical to our development. This video explains the different styles of attachment.
  • Piaget – Stage 1 – Sensorimotor stage : Object Permanence
    • This video shows the Piaget test of object permanence.
  • The Surprising Logical Minds of Babies- TED talk
    • How do babies learn so much from so little so quickly? In a fun, experiment-filled talk, cognitive scientist Laura Schulz shows how our young ones make decisions with a surprisingly strong sense of logic, well before they can talk.
  • What Do Babies Think- Ted Talk
    • “Babies and young children are like the R&D division of the human species,” says psychologist Alison Gopnik. Her research explores the sophisticated intelligence-gathering and decision-making that babies are really doing when they play.
  • Learning and Development of Language: The First 5 Years of Life 
    • In this video, we’ll look at four things known about Language Learning in general and then listen to the story of lucky Lucy and poor Pete to understand the importance of language in everyday life.
  • Noam Chomsky on Language Acquisition 
    • How is it that we learn to speak and think in language so easily? Philosophers have argued about whether or not we have innate ideas. Whether we are born knowing things, as Plato believed, or rather, as John Locke and other empiricists argued, the mind is a blank slate on which experience writes. Noam Chomsky gave a twist to this debate in the 1960s.
  • Schemas, assimilation, and accommodation | Khan Academy 
    • This video summarizes the concepts of assimilation and accommodation that take place during the sensorimotor stage.
  • “Good” and “Bad” are Incomplete Stories that we Tell Ourselves- TED talk 
    • Heather Lanier’s daughter Fiona has Wolf-Hirschhorn syndrome, a genetic condition that results in developmental delays — but that doesn’t make her tragic, angelic or any of the other stereotypes about kids like her. In this talk about the beautiful, complicated, joyful and hard journey of raising a rare girl, Lanier questions our assumptions about what makes a life “good” or “bad,” challenging us to stop fixating on solutions for whatever we deem not normal, and instead to take life as it comes.


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Lifespan Development Copyright © 2020 by Julie Lazzara is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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