Interesting.
The old fashioned way of child rearing, passed down from mother to daughter over many generations, included much more exposure to sunlight than current child-rearing methods. As children of the 1950s my siblings and I as babies would be put out in a pram in the garden to sleep every morning - regardless of weather - from day 1. In the afternoon we would be taken out in our pram for a walk. As toddlers we were turned out into the garden to play every morning and again, walks in the afternoon. As parents, we continued this regime with our own children. But it not so for my grandchildren. High rise living (no gardens) and mothers who have to work so children are put in nurseries where outdoor play is limited, mean that they have much less exposure to sunlight than previous generations. And at school we had much more outdoor activities than today's children. The emphasis on academic education has relegated sports activites to the tag end of the timetable instead of being an integral and daily essential. And social media and gaming has kept many teens indoors when in days gone past they would have engaged in outdoor ativities. And that's before considering the effects of slathering children with suncream as soon as the sun comes out from behind a cloud. It is not difficult to believe that the uptake of Vitamin D from sunlight via the skin has been extremely curtailed.