As far as I know, double jeopardy only applies to this particular boy. If he molested someone else, and it comes out, they should be able to try him for that.
I'm pretty sure double jeopardy only applies to these particular charges. If he were to molest the same boy again (however unlikely that may be), he could be charged and tried again for that crime, just not for the previous charges.
Double jeopardy only applies to charges already tried.