I read the first book in a series some time ago (10+ years) that involved a camp of kids that evolved powers and they weren't sure why.
I remember there was some planet-eating or larger creature slowly approaching Earth, and it turned out the powers were the result of some injured protector that was preparing the children in various ways to stop the threat. Or perhaps it was to heal the protector. I'm not sure if any more in the series actually came out.
I recall one kid had a long painful transformation where at one point he was ugly but came out in the end as something like the chosen one of the protector.