Misbehaving children are threatened with action from the Principal, a negative outlook on his disciplinary methods.
Randall Clark, from the overheard stories, states that, if the Principal comes to Zion Canyon in search of the missing children, he'll "blow his goddamn head off."
It's not confirmed, but it is a common theory that The Principal could be Borous as the acting Principal of the High School in Big MT. The Children could have been "experiment subjects" in his paranoia, as they fear the punishements of a cruel Principal. That mean they scaped from Big MT, something possible due to the fact they wouldn't be brainless and could pass through the fences of the crater.