A basic income guaranteed as long as you stay on birth control makes sense to me. Start paying a small amount at puberty. As soon as you have a child you lose access to it until your children are adults. This will work for men once we have reversible sterilization.
Honest question, what problems do you think this would solve?
Is it that you don't want people to have children until they are financially capable of supporting them?
It is indeed a grave responsibility to provide for one's offspring while they are still in the brood. But the upside of the situation, even in the unfortunate circumstance where one cannot make such financial provision, is no less than the creation of a brand new, fully conscious member of the human species, capable of experiencing the full wonder and surprise of being, who otherwise would have no chance of ever existing at all.
Furthermore, and here I risk delving into platitudes, children are quite literally the future of society. The continued production of children at a healthy clip is absolutely essential to the continuation of all the things we, as humans, value highest.
Hence it seems deranged to me to be so afraid of any monetary hardship that one should seek to positively disincentivize childbearing with such a broad and punitive measure. You are tampering with processes of infinite value and you do so at infinite risk.
As a smaller, more concrete objection, what about those who are initially of sound bank account, but then fall into hardship sometime after they've commenced in their procreative endeavours? Are they to be punished as well? In light of this possibility, why not take the opposite tack, and instead reward every new human life with a large gift to help pay for the cost of the upbringing?
This would solve so many problems in this world.