"There is abundant academic evidence on pro-natal policymaking: it is expensive, but it does work. If you spend a lot of money on the problem, financial and other incentives for having babies do increase the birth rate, albeit modestly. Some programs may be cheaper than others, in terms of increased birth rates per dollar spent. In general, programs that provide big cash lump sums, that target higher birth parities, and that are not politically divisive will have the biggest effect on births. So, the most cost-effective pro-natal policy would be something like $10,000 checks cut to all parents having their third or higher parity child, assuming you could get bipartisan support for such a policy."