A main source for the ages
Sleep Duration From Infancy to Adolescence: Reference Values and Generational Trends
Ivo Iglowstein, Oskar G. Jenni, Luciano Molinari, R. H. Largo · 2003 · PEDIATRICS
- Children
- About 500 children
- Where
- Zurich, Switzerland
- Ages
- Birth to 16 years
- How
- Parents' questionnaires as children grew
- What it found
- Nearly all children (96 in 100) still napped at 1½ years, and about a third still napped at 4.
- Limits
- We have only read the summary. It is one of the studies pulled together in the napping review, so it isn't a separate source.