Being in a rather formal prep school (with a large darkroom), I can say that horseplay is inevitable in any unsupervised (or supervised) situation. Let's just say the ceiling tiles above the film washer are a little stained :D On the other hand, there haven't been any bad incidents. It's mostly just fooling around and most of the stuff in the darkroom isn't toxic. Speaking of which, DO NOT GET ANY FILM CLEANER! Our school had one called PEC-12 or something which apparently gives chemical burns when sprayed on the bare skin of arms. Air dusters are also a very bad idea (compressed air, freezing liquid, highly flammable, will burn skin on hands when inverted) so I would stick with rubber pump bristled blowing brushes to control dust.
The kids are usually pretty focused on getting their projects done and doing things right so I'm not too worried about them messing around (especially if there is just one or 2 at a time!)