The fact they charged him with anything makes me sick.
Stop talking to us and talk to a lawyer, accept nothing -- I wouldn't, I would want to know how I could get him completely out of this e.g. he wasn't even smoking weed. That is what you need to work on.
Sounds like a scared kid to me. You haven't even stated whether he actually had anything on him at the time? I'm assuming he would have been charged with possession had he actually been caught with anything. Jesus, just see a lawyer -- why do people automatically assume they have to accept something? Especially in the case of a minor?
Fuck'em, he wasn't even stoned and has never even seed weed, stupid cops scared him, he was acting cool, whatever -- something irks me ya'know?