I read something too that it's far better to try and keep out of the direct sun, cover up and not go mad with the suncream.
I like my lot to run around uncreamed in the sun regularly. I use big floppy hats and cotton clothes,always keep out of the mid day sun, try to keep to shady areas etc. Never ever let them sit in full on blazing sun.
Obviously use sun suits and cream on the beach or where there is no shade. Always carry my cream incase it's needed. I think the chemical free creams work immediately rather than needing time to work-don't quote me though I could be wrong.
Anyhow none of them have ever burnt. They are only 3 and 4 though so it could change as they get older and I have less control.