Why? I'm not sure I'm properly understanding your point above. Why shouldn't families be obliged to actually make a claim for this sort of rebate? There is a growing culture of expecting money to just land in the bank account.
The rebate system seems better to me as it ensures that money intended to be spent on children actually is. The fact that people don't bother to claim the rebates is the parent's problem not the government's.
The just announced 'school kids' payment can just be regarded as another financial stimulus. If that's what it's intended for I don't disagree with it, but there is no guarantee it will be spent on school kids.