journal

PHYSICAL DEVELOPMENT

In

INFANCY and TODDLERHOOD

BODY GROWTH

During the first 2 years, the body grows more rapidly than at any time after birth.

By the end of the first year the infant’s length is 50 percent greater than it was at birth, and by 2 years

of age it is 75 percent greater.

Birth weight has doubled by 5 months of age, tripled by 1 year, and quadrupled at 2 years.

Research indicates that these height and weight gains occur in little growth spurts.

In infancy, girls are slightly shorter and lighter than boys. Ethnic differences in body size are apparent

as well.

Changes in Muscle-Fat Makeup

Body fat, which helps the infant maintain a constant body temperature, increases after birth and

peaks around 9 months of age.

Toddlers become more slender, a trend that continues into middle childhood.

Muscle tissue increases very slowly and does not peak until adolescence.

Girls have a higher ratio of fat to muscle than boys.

Skeletal Growth

Children of the same age differ in rate of physical growth.

Current body size is not

an accurate indication of

physical maturity.

Growth of the Skull

Because of the large increases in brain size, skull growth during the first 2 years is especially rapid.

At birth, the bones of the skull are separated by six gaps called fontanels.

Appearance of Teeth

• An infant’s first tooth usually appears between 4 to 6 months of age. By age 2, the average

child has 20 teeth.

• A child who gets her teeth early is likely to be advanced in physical maturity.

• 65 percent of teething infants show no symptoms.

– How often do infants find teething difficult and painful?

– If infants experience a difficult time teething parents usually know by the following:

• Changes in eating and sleeping routines

• A low grade temperature

• Drooling to an excess

• Biting on things

BRAIN DEVELOPMENT

The brain continues to develop at an astounding pace during infancy and toddlerhood.

Development of the Cerebral Cortex

The cerebral cortex is the largest structure of the human brain and accounts for 85 percent of its

weight.

It contains the greatest number of neurons and synapses, and it is the last of the brain structures to

stop growing.

Development of Neurons

The human brain has 100 to 200 billion neurons-nerve cells that store and transmit information.

Synapses are tiny gaps between neurons where fibers from different neurons come close together but

do not touch.

Neurons release chemicals that cross the synapse, thereby sending messages to one another.

• Neurons that are stimulated by input from the surrounding environment continue to establish

new synapses

• Myelinization is a process in which neural fibers are coated with an insulating fatty sheath

(myelin) that improves the efficiency of message transfer.

• Glial cells make up about half of the brain’s volume and do not carry messages; their most

important function is myelinization.

Changing States of Arousal

• During the first 2 years, the organization of sleep and wakefulness changes and fussiness and

crying also decline.

• Over time, infants remain awake for longer daytime periods and need fewer naps.

• Although brain maturation is largely responsible for changes in sleep and wakefulness, the

social environment also contributes. By the middle of the first year, melatonin secretion in the

brain is greater at night.

The practice of isolating infants to promote sleep is rare outside of the United States and other

Western nations.

Even after infants sleep through the night, they continue to wake occasionally for the next few years.