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 rapid infant and early toddler growth, growth slows until the adolescent growth spurt Physical Growth and Sexual Maturation of Adolescents During adolescence (usually considered age 10 to the late teens), boys and girls reach adult height and weight and undergo sexual maturation ( puberty). The timing and speed with which these... read more . 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 Sexual Maturation (Puberty) During adolescence (usually considered age 10 to the late teens), boys and girls reach adult height and weight and undergo sexual maturation ( puberty). The timing and speed with which these... read more (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.
Doctors report how children are growing in relation to other children their age and monitor the children's weight gain compared to their height. From birth until 2 years of age, doctors record all growth parameters in a chart by using standard growth charts from the World Health Organization (WHO). After age 2, doctors record growth parameters by using growth charts from the Centers for Disease Control and Prevention (CDC).
(See also Health Supervision of the Well Child Promoting Optimal Health and Development of Children Parents can help their children achieve their best possible health. The foundation for a healthy body and mind is laid in early childhood. The early years of life are crucial for health and... read more and Failure to Thrive Failure to Thrive in Children Failure to thrive is a delay in weight gain and physical growth that can lead to delays in development and maturation. Medical disorders and a lack of proper nutrition are causes of failure... read more .)
Length and Height
Length is measured in infants. Height is measured in children who can stand. Infants are placed on their back on a suitable device, such as a measuring table (called a supine stadiometer), and children who can stand are measured using a vertical or standing stadiometer.
In general, length in full-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. Most boys reach half their adult height by about age 2 years. Most girls reach half their adult height at about age 19 months.
(See also growth charts for children birth to 2 years old from the WHO and growth charts for children and adolescents 2 to 20 years old from the CDC.)
Weight
Full-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.
Since the 1980s, more children in the United States have developed obesity Obesity Obesity is excess body weight. Obesity is influenced by a combination of factors, which usually results in consuming more calories than the body needs. These factors may include physical inactivity... read more 
(excess body weight), and the number of children and adolescents with obesity remains high today. Some children become obese at an early age. The body mass index (BMI) is used to define overweight and obesity. The CDC has released extended BMI-for-age growth charts for boys and girls who have a very high BMI.
(See also growth charts for children birth to 2 years old from the WHO and growth charts for children and adolescents 2 to 20 years old from the CDC.)
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.
Teeth
The timing of tooth eruption varies, mainly for hereditary reasons. However, tooth eruption may also be delayed by disorders such as rickets Hypophosphatemic Rickets Hypophosphatemic rickets is a disorder in which the bones become painfully soft and bend easily because the blood contains low levels of the electrolyte phosphate. (See also Introduction to... read more , hypopituitarism Hypopituitarism Hypopituitarism is an underactive pituitary gland that results in deficiency of one or more pituitary hormones. Symptoms of hypopituitarism depend on what hormone is deficient and may include... read more , hypothyroidism Hypothyroidism Hypothyroidism is underactivity of the thyroid gland that leads to inadequate production of thyroid hormones and a slowing of vital body functions. Facial expressions become dull, the voice... read more 
, or Down syndrome Down Syndrome (Trisomy 21) Down syndrome is a chromosome disorder caused by an extra chromosome 21 that results in intellectual disability and physical abnormalities. Down syndrome is caused by an extra chromosome 21... read more 
.
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 2½ 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 symptoms caused by tooth eruption (such as drooling and fussiness) are called teething Teething A child's first tooth usually appears by 6 months of age, and a complete set of 20 primary or first teeth usually develops by 2½ years. Before a tooth appears, the child may cry, be fussy, and... read more .
More Information
The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.
World Health Organization (WHO): Growth charts from the WHO for infants and children ages 0 to 2 years of age
Centers for Disease Control and Prevention (CDC): Growth charts from the CDC for children and adolescents age 2 years and older in the United States
CDC: Extended BMI-for-age growth charts for boys and girls who have a very high BMI
