Yeah, it would be pretty much impossible for anything to come back to you. The worst he could do, if he's a pretty smart kid, is to "Transfer Purchases" back to his home computer. And then to play them he'd have to enter your account info and password. It wouldn't even prompt a name, I don't think, he would have to know the name and password combo to get anything out of them. Without them they're useless on a random computer.
But yes, if you poke around and deauthorize all computers, as mentioned above, even if somehow he does obtain/figure out your password and username.