Weblette
My DC are 9yo and 6yo and we live in Geneva so see a fair bit more sun that the average Scot. :)
We have a family in the village whose children are slathered in sun cream even if they are out in the sun for just 15 mins - they were the only pale children in school last September as most of the locals seem to do the same as we do - if we are at the beach all day, I smear them in SPF 20 (anything higher than that has been proven to be no more effective so I see no point in paying more for it). At the beginning of the summer, I expose them gradually to the sun, for just 10 - 20 mins at first.
I can always spot the Brits at the beach as they are the ones with sunshade tents and UV clothing.
We don't go to the beach over the midday period and sit in the shade of large trees.
Last year my parents took the DC to the beach and disregarded my rules (not deliberately, they just didn't think) but still put suncream on them. The DC were out in the sun all day without hats and got severe sunstroke. I was close to taking DD to A&E.
Obviously, if your children are extremely sensitive to sunshine then you have to protect them, but I do believe that exposing them to small amounts is better.
The danger is that if you are caught out and forget to use suncream (or are out for the day and the sun comes out unexpectedly, the children who have had no sun exposure will be more likely to burn than those who are naturally protected.
Btw, I read this recently about the link between MS and Vit D/Glandular fever.