Physical growth refers to an increase in body size (length or height and weight) and in the size of organs. From birth to about age 1 or 2 years, children grow rapidly. After this time, growth slows. As growth slows, children need fewer calories and parents may notice a decrease in appetite. Two-year-old children can have very erratic eating habits that sometimes make parents anxious. Some children may seem to eat virtually nothing yet continue to grow and thrive. Actually, they usually eat little one day and then make up for it by eating more the next day.

During the preschool and school years, growth in height and weight is steady. Children tend to grow a similar amount each year until the next major growth spurt occurs in early adolescence.

Different organs grow at different rates. For example, the reproductive system has a brief growth spurt just after birth, then changes very little until just before sexual maturation (puberty). In contrast, the brain grows almost exclusively during the early years of life. The kidneys function at the adult level by the end of the first year.

Children who are beginning to walk have an endearing physique, with the belly sticking forward and the back curved. They may also appear to be quite bow-legged. By 3 years of age, muscle tone increases and the proportion of body fat decreases, so the body begins to look leaner and more muscular. Most children are physically able to control their bowels and bladder at this time.

Length and Height

Length in children who are too young to stand is measured while children lie on their back on a suitable device, such as a measuring table (called a stadiometer). Height in children who can stand is measured using a vertical measuring scale. In general, length in normal-term infants increases about 30% by age 5 months and more than 50% by age 12 months. Infants typically grow about 10 inches (25 centimeters) during the first year, and height at 5 years is about double the birth length. In boys, half the adult height is attained by about age 2. In girls, height at 19 months is about half the adult height.


Normal-term newborns typically lose 5 to 8% of their birth weight during the first few days of life. They regain this weight by the end of the first 2 weeks. After this period of time, newborns typically gain about 1 ounce per day during the first 2 months, and 1 pound per month after that. This weight gain typically results in a doubling of birth weight by age 5 months and a tripling by 1 year. In recent years, more children have developed obesity. Some children become obese at an early age.

Head circumference

Head circumference is measurement around the largest area of a child's head. Doctors place the tape measure above the eyebrows and ears and around the back of the head. This measurement is important because the size of the head reflects the size of the brain, and this measurement lets doctors know whether the child's brain is growing at a normal rate. Head circumference is routinely measured until children are 3 years old.

At birth, the brain is 25% of its future adult size, and head circumference is about 14 inches (about 35 centimeters). By 1 year of age, the brain is 75% of its adult size. By 3 years of age, the brain is 80% of its adult size. By 7 years of age, the brain is 90% of its adult size.


Lower front teeth usually begin to appear by the age of 5 to 9 months. Upper front teeth usually begin to appear by 8 to 12 months. On average, infants have 6 teeth by age 12 months, 12 teeth by 18 months, 16 teeth by 2 years, and all 20 of their baby (deciduous) teeth by 2 years. Baby teeth are replaced by permanent (adult) teeth between the ages of 5 years and 13 years. Permanent teeth tend to appear earlier in girls.

The following chart focuses on reflexes of the developing infant.




Age of disappearance


Eye blink

Bright light shining in eyes or clap hands by eyes

closes eyelids quickly


This reflex protects the infant from a lot of stimulation


Stick sole of foot with stimulus like a pin

This causes the foot to withdraw, this occurs with the use of flexing of the knee to hip

Decreases after the 10th day of birth

This is a protection for the infant in the instance of unpleasant tactile stimulation


Touch cheek near the corner of the mouth

The infants head will turn towards the site of stimulation

3 weeks (due to the voluntary response that is now capable for infant to do at this time)

This reflex helps baby to find the mothers nipple


Place fingers in infant's mouth

The infant will suck finger rhythmically

4 months (voluntary sucking will come about)

This helps with feeding


Place the baby in pool of water face down

The baby paddles and kicks in swimming movements

4 to 6 months

This helps baby to survive if dropped into the water


Hold infant in a cradling horizontal position and slightly lower the baby in a fast motion toward the ground while making a loud sound supporting the baby

The baby will make a embracing motion and arch its back extending its legs throwing its arms outward, and finally it will bring arms in toward its body

6 months

In the evolutionary past this may have helped the baby cling to the mother

Palmar grasp

Place the finger in baby's palm and press against the palm

The baby will immediately grasp the finger

3 to 4 months

This prepares infant for when voluntary grasping comes about

Tonic neck

Turn the baby's head to one side while the baby is awake

This will cause the baby to extend one arm in front of its eye on one arm to the side to which the head has been turned

4 months

This may prepare for voluntary reaching


When you hold the baby under the arm and permit the bare feet of the baby to touch a flat surface

The baby will lift one foot after the other in a stepping fashion

2 months (this applies to a baby who has gained weight a baby who is not as heavy this reflex may be submissive)

This prepares the baby for voluntary walking


Touch the foot in a stroking manner form the toe toward the heel

The baby's toes will fan out and curl as the foot twists in

8 to 12 months