why?
EDIT: I think that the 10pm/midnight cutoff point is less about some danger switch getting flipped at midnight and more about there being some well-defined point where CPS need to step in and ask the parents why their children are unsupervised. If it's vaguely defined it makes enforcement of the law more difficult or will cause the law to be unevenly applied (something like poor kids get neglected because CPS can't prove neglect).