A main source for the ages
Assessment of sex differences and heterogeneity in motor milestone attainment among populations in the WHO Multicentre Growth Reference Study
WHO Multicentre Growth Reference Study Group · 2006 · Acta Paediatrica
- Children
- About 800 children
- Where
- Ghana, India, Norway, Oman and the United States
- Ages
- 4 months to 2 years
- How
- Compared boys with girls, and the five countries, in the same children
- What it found
- Boys and girls reached these milestones at the same ages. There were some differences between countries, probably from different ways of caring for babies, and Norwegian children were latest on average for all six.
- Limits
- Same children as the main WHO study, so it isn't an independent second source.