If it's a real looking gun, then I can see some kind of charge, but not the same as if a real one is aimed at someone. Those kids are lucky they didn't get shot. If it looked real and someone had reasonable fear for their life, it would be a justified shoot.
Here the offence is "pointing a firearm" whether it's real or not because both the intent and the effect are the same in either case. It is usually applied in robber-using-toy-gun situtions but if one points a gun at someone to intimidate then the charge SHOULD be the same as with a real one. In criminal law, intent is everything. These are hardly children we're talking about- at 13 they should know better.