Table 1 Illustrates the variable definitions used and overlap of different age groups of children

Preterm neonate

Period at birth when a newborn is born before full gestational period.

Term Neonate

Birth to 27 days.

Newborn up to 1 month.

A newborn infant, or neonate, is a child under 28 days of age.

Infant/Infancy

28 days to 1 year of age.

1 month to 2 years.

0 to 1 year of age.

Toddler

13 months to 2 years.

1 to 3 years.

Preschool child

3 to 5 years.

Early childhood

2 to 5 years.

Middle childhood

6 to 11 years.

Child

2 to 12 years.

Young teen

12 to 14 years.

Teenager

15 to 17 years.

Adolescent

12 to 16 years.

10 to 19 years.

Early adolescence

12 to 18 years.

Late adolescence

19 to 21 years.