I am English, but have fairly dark skin due, in part, to my ancestry. I sit in the sun for 20 minutes and turn brown. That's me. My wife, a traditional English rose, as such, needs two weeks in the sun to turn white after each winter. Each person's skin is different, and that goes to their kids too. I have 3 kids. One of them has good olive skin, so we don't mind her being in the sun for any period of time; she doesn't burn. The next, like the wife, has quite sensitive skin, so we keep our eyes on her more. The other, like me, has fairly dark skin, for an English person, so, again, we don't tend to worry about her more.
However, The most important source of vitamin D is not food, it's sunlight. Vitamin D isn't actually a vitamin, it's a steroid hormone that the body produces using UVB rays from the sun. Vitamin D deficiences in babies can arise if babies receive inadequate exposure to sunlight.
The American Academy of Pediatrics recommend all breastfed babies be given vitamin D supplements. This is because, they say, breast milk does not contain enough vitamin D (or sunlight maybe?)
Read more: http://www.homemade-baby-food-recipes.com/baby-and-vitamin-D.html#ixzz1M1ksDh83
Read more: http://www.homemade-baby-food-recipes.com/baby-and-vitamin-D.html#ixzz1M1kSx3Kt
Anecdotally, as a kid, I was blond, blue eyed and spent 12 hours a day semi naked (just in shorts) in the sun, fishing, playing sport, sitting about, swimming and I never burned. I do think we tend to worry about too many things nowadays. I think an element of common sense is needed here; if it is 32 degrees outside and bright sunlight, don't let the kids play outside for too long without some kind of lotion on. If it is 18 degrees and not so sunny, whilst you do have to keep an eye open, it's not so bad.
"To make enough vitamin D, a baby in a diaper [nappy] needs a total of only 30 minutes of sunlight a week-less than five minutes a day. Fully clothed and without a hat, a baby would need two hours of sunlight a week, or about 20 minutes a day. Medium to darker skin tones need a little more time in the sun."