I'm a little surprised at how worried everyone is. In general the plate glass in a tank is no more fragile than the plate glass in a window. A tempered glass tank would be even better, but just teach the kid not to throw things at the tank because it might kill the fish. I'd skip a full blown reef with a sump and MH, but a self contained tank with overflows in the back, a couple of PHs and some T-5's would be glorious! A couple of clownfish, maybe some colorful gobies and a firefish or two. Safety is good, you shouldn't just put any old tank in any old stand (a cabinet and a hood that locks, with a key that you keep safe, and the wiring all contained, and everything screwed to the studs through the wall would be grand) but kids need to be stimulated too.