In the Nordic countries at least, kids spend quite a lot of hours of the day outside in nursery/kindergarten/school as a rule (babies too: https://www.bbc.com/news/magazine-21537988 ) while as parent comment writes, school systems that encourage less outdoor time lead to more myopia.

There's less sunlight in the North during the winter, sure, but still several orders of magnitude more than inside (also, more UV etc.).