A main source for the ages
Similarities and differences in child development from birth to age 3 years by sex and across four countries: a cross-sectional, observational study
Ilgi Ozturk Ertem, Vibha Krishnamurthy, Mphelekedzeni C. Mulaudzi, Yanina Sguassero, Hakan Balta, Ozlem Gulumser · 2018 · Lancet Global Health
- Children
- About 4,900 healthy children
- Where
- Argentina, India, South Africa and Turkey
- Ages
- Birth to 3½ years
- How
- Trained staff asked parents open questions about what their child could do, at health clinics
- What it found
- Found the age by which half of children reached more than 100 milestones. Most came at similar ages in all four countries, and for boys and girls. For example, half of children waved bye-bye by about 11 months and said a first word by about 9 months.
- Limits
- Only four countries and no rural areas, children from city clinics, and only healthy children (about half of those who came were left out for health reasons). It gives the age for half of children, not the full spread.