Infant development is the earliest stage of a child's development after birth. In general, the term infant refers to babies between 0 to 12 months old. The following will help you learn the major changes that occur to humans during infant development, problems that may arise during this stage, and ways to help support healthy development during this stage.

What occurs during infant development?

There is a lot of individual variation among infants regarding behaviors like sleep/wake patterns and eating. However, there are typical behaviors that are characteristic of most all infants. For one, lots of sleeping is typical as infants spend the majority of each day (16 to 18 hours) asleep¹. Young infants are only actively awake and alert enough to interact with others for about one total hour each day. As babies grow through the first year of life, their sleep patterns shift and many can sleep through the night by 6 months of age¹.

Eating every three to four hours is also typical of infants due to their small stomachs¹. Also, lots of crying is to be expected as it is a form of communication for infants. The average 3-month-old cries for about one total hour each day². Infants use cries to signal things like hunger, sleepiness, and distress². Most babies reach their peak amounts of crying around 6 weeks of age². According to Zero to Three², the condition called colic is characterized by infant crying:

• Begins/ends for no obvious reason
• Lasts at least three hours daily
• Happens at least three days per week
• Continues for three weeks to three months

Research has shed light on the developmental milestones, or typical growth changes, which occur for infants. The following chart summarizes the major milestones that occur between birth and 12 months of age, broken down by the major domains of child development:

Domain:	Milestones between 0-3 months:
Physical	Can grip objects and fingers
Cognitive	Shows signs of learning (e.g., how caregivers will respond to cries)
Emotional & Social	Begins recognizing faces, voices, smells; begins showing early signs of responding to others; relies on caregivers for calming distress
Language	Communicates through sounds (e.g., crying) and facial expressions; Can begin to express needs (e.g., hunger) and emotions (e.g., distress, happiness)
Domain:	Milestones between 3-6 months:
Physical	Can begin pushing body up, rolling, rocking, and sitting up with assistance; uses fingers and mouth to grasp objects and explore
Cognitive	Learns about things in his/her immediate environment through observation and exploration; can pick up on daily routines (e.g., bed time)
Emotional & Social	Engages more with people around him/her through sound and facial expressions; more ability to self soothe when distressed
Language	Communicates through more sounds than before (e.g., laughter, cooing) and facial expressions
Domain:	Milestones between 6-9 months:
Physical	More control over body (e.g., fine motor skills, can sit on his/her own, crawling, scooting)
Cognitive	Learns more through observation and imitating others; thinking skills progress (e.g., learning to solve basic problems like finding a toy)
Emotional & Social	More ability to express feelings through tone of voice and speech; begins showing personality and social preferences more (e.g., discomfort with strangers) Interested in learning more? Why not take an online Early Childhood Development course?
Language	Communicates through more sounds
Domain:	Milestones between 9-12 months:
Physical	Can travel more through crawling, scooting, standing, and walking, in many cases
Cognitive	Can follow basic directions (e.g., "come here"); can understand that people and objects still exist, even when they are out of sight; can build memory through repetition/practice
Emotional & Social	May cry whenever caregivers leave and want to cling; can build trust that caregivers will return
Language	Can understand more words than he/she can speak; can form basic words (e.g., "dada" and "mama")

Source: Adapted from Zero to Three fact sheets ^{2, 3, 4, 5}

What problems may arise during infant development?

Premature birth refers to the birth of a fetus before reaching the gestational (in womb) age of 37 weeks¹. About 12 percent of infants in the U.S. are born premature each year and such births comprise approximately 70 percent of newborn deaths¹. However, with modern medical care provided through neonatal intensive care units (NICU), many premature infants have high survival rates. Although there are higher survival rates than ever before, prematurity comes with a number of health risks for infants, including developmental delays¹ (e.g., cognitive deficits, physical disabilities). However, prematurity does not guarantee that developmental problems will occur, as many premature infants show typical development later in life.

Low birth weight is another problem that may arise during infant development. While many premature infants have low birth weight by virtue of being born before reaching full term, what qualifies as low birth weight is determined by the gestational age¹. For full term babies (babies born after 37 weeks gestational age), low birth weight is defined as under 5 pounds, 4 ounces¹. Having low birth weight is another potential of developmental problems for infants.

Birth defects are yet another problem for infant development. According to the U.S. Centers for Disease Control and Prevention, about 120,000 babies experience birth defects annually⁶. Birth defects may be identified before or after a baby is born and affect any body part or organ. Their causes may be genetic or due to prenatal stressors (e.g., substance use of the mother during pregnancy). Examples include cleft lip and heart abnormalities.

Infant mortality is another major consideration for the development of infant. It is defined as a death that occurs within the first year of life¹. On average, 6.4 out of 1,000 babies experience infant mortality in the U.S. which is one of the highest infant mortality rates of all developed countries¹. By comparison, this same rate is 5.3 in Canada, 3.9 in Spain, and only 3.2 in Japan. A major cause of infant mortality is a condition called sudden infant death syndrome, or SIDS. SIDS is defined as an unexpected death of a healthy infant and it most often occurs between 2 to 4 months of age¹. To date, exact causes for SIDS are unknown although there are identified risk factors such as improper sleep positions (e.g., having infants sleep on their backs has reduced SIDS rates).

One way to help support healthy infant development is through preventative screening. Infant screening is standard practice within the U.S. health care system and is done routinely right from birth throughout the first year of life to help detect problems like hearing loss, brain damage, diseases (e.g., hypothyroidism) and physical abnormalities⁷.

Another way to help support healthy infant development is through healthy caregiving practices⁸. For examples, parents and other caregivers can help infants learn communication skills through talking and reading to them. Also, emotional and social development can be supported by holding and cuddling babies, as this helps them form secure attachments to their caregivers.

Introduction

Physical development is a major domain of early childhood development. It encompasses the biological development of the body (growth, organ development) and skills that are performed using the body. The following section covers the key areas of knowledge one should have in regard to early childhood physical development, including the development of the body, motor skills, senses, and brain.

Body Development

Early childhood development is a time of many rapid physical changes. The body grows quickly in terms of size and weight, especially between birth and 2 years of age¹. The bones grow rapidly and the size of the head -- which is proportionally very large at birth -- begins to become more proportionate to the rest of the body. The amount of physical growth that occurs and the ultimate outcomes, such as adult height, are dependent on both "nature and nurture," as both genetics and environmental influences (e.g., proper nutrition) play a role.

One example of a major physical change that occurs in early childhood is the growth of teeth. This usually happens within year one of development and is referred to as teething. In early childhood, children eventually lose their baby teeth, around age 6, to make way for adult teeth to grow.

Motor Skills

Because the development of these skills takes time, infants are born with certain bodily reflexes (involuntary responses) that help them do things like suck while feeding and grasp fingers. The following table outlines examples of infant reflexes and examples of those that continue into adulthood:

Reflex	Description
Babinski reflex	When the foot sole is touched, an infant's toes spread out
Startle reflex	Infant extends arms then pulls them toward body and cries briefly in response to loud noises
Palmar hand grasp	Infant grips a finger or object placed in his/her hand
Rooting and sucking	Infant turns head to search for a nipple in response to a cheek touch; begins to suck when a nipple touches the lip
Reflexes that continue into adulthood:
Blinking reflex	Blinking in response to bright light or an eye touch
Cough reflex	Coughing in response to airway irritation
Gag reflex	Gagging in response to the stimulation of the throat or back of mouth
Sneeze reflex	Sneezing in response to the irritation of nasal passages
Yawn reflex	Yawning in response to the need for more oxygen

Source: Adapted from information provided by the National Institutes of Health²

Senses

Another key physical change that occurs in early childhood is the development of the five senses. These include vision, hearing, taste, touch, and smell. Regarding sight, babies are born with 20/400 vision (compared to 20/20 vision for adults)¹. In other words, newborn babies can see at a length of 20 feet at the same level of accuracy that an adult can see at a length of 400 feet. Between the ages of 6 months and 3 years, sight begins to improve toward adult levels.

Brain Development

Brain development is another critical area of physical development that occurs during early childhood. The brain first begins development within two to three weeks of conception and continues throughout early adulthood³. It is fully matured by early adulthood. Both "nature and nurture" shape how the brain develops. Genetic influences impact how the brain circuitry is wired, such as neurons and connections between regions, while environmental factors like nutrition, life experience, and stress shape the exact architecture of the brain over time³.

Key terms related to early brain development include plasticity and pruning. Plasticity is the brain's ability to grow and change over time¹. Humans are born with high brain plasticity and thus the ability to learn very rapidly^{1, 3}. This makes children, especially very young children highly impressionable and while this is very valuable for learning, this high plasticity makes their brains vulnerable to problems if problems occur during early development such as trauma, high stress, or environmental toxins^{3, 4}.

Source: Center on the Developing Child at Harvard University⁵

In addition to plasticity, pruning is another key term related to early brain development. Pruning is a process which involves the selection of particular neural circuits within the brain through experiences^{1, 3}. As new brain connections are made, for example through learning certain language or playing a musical instrument, certain pathways are formed. If these connections continue to be used, they are retained over time while those that are not used eventually break down and disappear¹. In other words, it is the idea of "if you don't use it, you lose it." Most pruning takes place in early childhood.