The most important and sensible thing to do would be to not do this, and to take the additional $2.6 billion per year that this would cost and put it toward the most important benefit that would assist people trying to lift their children out of poverty going forward.
If it were necessary to do some form of this, then it really should be completely cast as a refundable type of credit. It should absolutely be cut off very close to the phase-out point at which something like the Canadian child tax benefit is phased out, or at the most, the $112,000 level for the phase-out of the OAS. It should be reversed in effect, because to give $39 per year to people with the lowest incomes and $4,700 per year to people with the highest incomes is unethical.