The logic is they're kids, they're not old enough to deal with some of the stuff Bobby throws at camp goers and they're not legally old enough to make those choices themselves or handle guns and the like.
The classes offered, all of them, are up to those who teach them and Bobby's said no. That's it.
And yes, before you say it, a demon can possess a kid same as anyone else, but its the job of those older to protect the kids from that. They should never have been brought by the seal in the first place, but they have been and so we need to account for that.