Biosocial Developmental Milestones from Birth to Age 2

This is the first of a series of articles on child development from birth to 2 years. Child development is not an exact science. Every infant grows and develops at its own pace. However the information provided in this article are a useful reference for every new parent.

1. Body Shapes and Dimensions

At birth, the average baby measures 50cm and weighs just over 3.4kg. By 1 year, children weigh about 10kg and measure almost 75cm. By 2 years, children have reached about half of their adult height and 90% of adult head size.

2. Growth and maturation of the brain

At birth, a baby's brain is at 25% of its adult weight. By 2 years a child's brain has reached about 75% of its adult weight. The developmental changes occurring between birth and 2 years are particularly significant.

During the first few months and years, the brain undergoes important modifications that improve its functioning. Among the most important changes is the growth of communication between its billions of cells, called dendrites. Neurons and dendrites are coated by an insulating lipid substance called myelin, which makes the transmission of nerve impulses more efficient.

3. The regulation of physiological states

An important function of the brain during life is the regulation of physiological states. Normally newborn babies experience 3 physiological states: quiet sleep, with regular and slow breathing where the muscles appear relaxed; active sleep, in which the facial muscles contract and breathing is rapid and less regular; and a state of vigilance, where the eyes are lively and breathing is rapid and relatively regular.

As the brain develops, the baby's physiological states become more cyclical and separate. Between birth and 12 months the amount of daily sleep does not change much, from 15 to 13 hours of sleep, but the duration and frequency of sleep episodes become more similar to those of the rest of the family.

4. Sensory development

Babies' sensory experiences are really important for the development of their sensory abilities. The basic elements of a child's sensory systems are largely already determined at birth.

- Vision

Babies' vision is constantly developing as they grow. At birth, vision is the least developed of babies' senses. A newborn baby can quickly focus on objects that are between 10 and 75 cm away. Within the first 3 months the ability to use both eyes together to focus on an object develop; as a result, the perception of depth and movement is greatly improved. By 6 months, a baby is able to use both eyes to follow a moving object and both hands to grasp steady objects, but they still are unable to show eye-hand coordination. By 8-9 months babies are able to adjust the movement of their arms and hands to grasp an object. By 2 years they are able to successfully grasp a moving object.

- Hearing

A baby's hearing is very sensitive. Sudden noises scare a baby; rhythmic sounds, like a lullaby, calm them down and make them fall asleep. When they are awake, they usually turn their head in the direction of a noise and are particularly attentive to people' s conversations. At three days after birth, a newborn can distinguish his mother's voice. By 1 month, children are able to differentiate similar sounds. By 6 months, their hearing is less sensitive to low-frequency sounds.

- Taste and smell

Taste and smell develop jointly during the first few months and improve significantly by 1 year. By the end of infancy, these senses are at their best that at any other time during life.

5. Motor skills

Due to changes in body size and brain, children quickly develop the ability to move and control their body. Gross motor skills (which allow the child to run and climb and require large movements), and fine motor skills (which consist of small and precise movements), develop rapidly during the first two years. Thanks to gross and fine motor skills children become more and more independent as they start to explore their environment.

- Reflexes

Children's first motor skills are involuntary responses to particular stimuli. Newborn babies have dozens of reflexes: some are essential to life itself; others disappear in the months after birth; others lay the foundations of subsequent motor skills.

Three sets of reflexes are crucial for survival and become stronger as babies grow. Some guarantee an adequate amount of oxygen. The most obvious reflex of this group is the breathing reflex: children usually make their first breath even before the umbilical cord is cut. During the first few days, breathing is somewhat irregular. Another group of reflexes helps to maintain a constant body temperature: when the child is cold, he cries, shakes and bends his legs, moving them closer to his body, thus helping to preserve his heat.

A third group of reflexes supports feeding. The sucking reflex is the reason why babies tend to suck anything with their lips. Another reflex of this group is the baby's search for food, which causes them to turn their head to the side and begin to suck when something rubs against their cheek. Swallowing is another important reflex that helps feed, as is crying when a baby's stomach is empty.

Other reflexes are not necessary for survival, but they are important signs of normal physical and cerebral functioning.

- Gross motor skills

A newborn baby lying on his stomach moves his arms and legs as if he was swimming and tries to lift his head to look around. As he gains muscle strength, he begins to wriggle and tries to move forward, pushing his arms, shoulders and upper body against the surface on which he is leaning. By 6 months, babies become able to use their arms and legs to slowly crawl forward. Between 8 and 10 months, most children coordinate the movements of their  hands and knees in a fluid and balanced manner. On average at 9 months a child can walk if held by their hands, at 10 months can stand alone for a few moments and by 12 months can walk independently. Upright mobility offers a new view of a baby's environment and frees his hands, boosting fine motor skills' development.

- Fine motor skills

By 2 months, babies are able to move their arms towards an object that oscillates in their visual field and by 3 months, they can touch it. At 6 months, most children can reach, grab and hold almost any object of appropriate size.

A 6-month-old baby has mastered a wonderful eye-hand-mouth exploration system, which is sufficiently developed to allow them to hold an object in one hand and touch it with the other, and turn it over and over in order to examine it. At the same time babies develop the ability to hold and manipulate small objects. Between 9 and 14 months, children also acquire the ability to use their thumb and index together.

- Variations in motor development

Although all healthy children develop the same motor skills in the same sequence, the age at which these skills are acquired may vary from child to child. Research shows that the age when a child exhibits a particular ability for the first time depends on the interaction between hereditary and environmental factors. 

The fact that a child is a little early or late in walking or in any other motor capacity is completely irrelevant to development; however, if a significant delay occurs, it is advisable to consult with an expert.

6. Feeding

Frequency of feeding is not a crucial factor. Proper nutrition is essential for physical growth, brain and motor skills development at this early stage of life.

Babies double their weight during the first few months of life. In these first months, breast milk is babies' ideal food. Brest milk contains more iron, vitamin C and vitamin A than cow's milk. It also contains antibodies that provide the child with some protection against diseases.

It is important to gradually start introducing solid foods to babies' diet at 6 months. By 1 year, their diet should include all the foods eaten by the rest of the family.

The next article in this series will focus on children's cognitive development from birth to age 2.