What are the different age groups in children and their definitions?

Pediatric Age Group Definitions

The most widely accepted and standardized pediatric age definitions are: infant (0-1 year), child (2-12 years), and adolescent (13-18 years), as consistently used across multiple American Academy of Pediatrics clinical guidelines. 1

Standard Age Categories

Infants

• 0 to 1 year of age 1
• This represents the first year of life and is universally recognized across pediatric subspecialties

Children

• 2 to 12 years of age 1
• This encompasses the preschool, school-age, and pre-adolescent periods
• Some guidelines use overlapping ranges (e.g., 0-5 years for early years, 5-17 years for school-age), which can create ambiguity in application 1

Adolescents

• 13 to 18 years of age (standard pediatric definition) 1
• 10 to 19 years (WHO definition) 2
• 10 to 21 years (extended clinical definition used in adolescent medicine) 2

Important Nuances and Variations

Extended Adolescent Care

• Adolescent medicine clinicians and school health providers often continue care until age 21, recognizing that developmental maturity extends beyond the traditional 18-year cutoff 2
• For patients aged 18-21 years, providers may use either adult or adolescent guidelines based on the individual's developmental status 2
• Arbitrary age limits should be discouraged—the decision to continue pediatric care should be made by the patient, family, and physician based on physical and psychosocial needs 3

Youth vs. Adolescent Terminology

• "Youth" specifically refers to ages 15-24 years according to WHO and United Nations definitions 1, 2
• This term should NOT be used interchangeably with "adolescent" as it creates confusion 1
• Terms like "young people" lack precision and should be avoided in clinical contexts 1

Critical Pitfalls to Avoid

Overlapping Age Ranges

• Some countries use overlapping categories (e.g., Netherlands: 0-4 years AND 4-18 years; Australia: 0-5 years AND 5-17 years), which creates ambiguity about which guideline applies to children at the boundary ages 1
• When encountering overlapping ranges, use developmental stage (e.g., school attendance) rather than age alone to determine appropriate guidelines 1

Subjective Categories

• Avoid vague terms like "school-aged children" or "pre-pubertal" without specific age ranges, as these lack the clarity needed for clinical decision-making 1
• Cultural differences in formal schooling can make school-based categories unreliable across populations 1

Preschool/Early Years Subgroup

• Some guidelines specifically define 0-5 years as "early years" or preschool age, recognizing this as a distinct developmental period 1
• This subgroup is particularly important for developmental screening and early intervention services 4

Developmental Considerations

• Physical development and autonomy vary significantly between individuals of the same chronological age 2
• Children with chronic diseases may develop autonomy later than their peers, requiring flexibility in age-based care transitions 2
• There is a notable decline in physical activity as children transition from childhood to adolescence, marking an important behavioral shift during this period 1, 2