What's this book called?

I can’t remember any of the characters’ names, which would probably help alot…...

This boy lived on a raft in an underground river, & got to the outside world somehow, but couldn’t get back in. The book covers his adventures in the outside world, & his attempt to get back to his family.

A scene at the beginning I remember: He ate a peach, then fell asleep in the sun. When he woke up with a bad sunburn, he was freaking out & some girl found him. They had kinda funny names….