Table 1

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

Name	Definition
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.

^a NICHD Eunice Kennedy Shriver National Institute of Child Health and Human Development

^b FDA US Food and Drug Administration

^c WHO World Health Organisation

^d CDC Centers for Disease Control and Prevention