Nah this is socially engineered, america had its baby boom because it was rich. Africa doesn't have one because it's poor: it had one because America and other rich nations subsidize these poor populations to reproduce.
We spend about 1000 bucks per 18-35 year old American on foreign aid per year and about 1500 bucks per 18-35 year old on SNAP benefits. We also spend about 20k per 18-35 year old per year paying out social security retirement benefits, which are expected to be exhausted in 8 years.
So for the same amount we are spending right now on soda, old people, and foreigners, we could (theoretically) restructure that spending to be giving families with at least one working parent and additional $30,000 post-tax stipend for being good tax unit producers per year and save money compared to what we are doing now. And that's assuming every 18-35 year old is evenly distributed by sex and 100% of them decide to settle down and start popping out kids when they see a free Toyota camry each year dangling in front of them.
Obviously that's not how you it could.work in practice but the point is developed nations or at least the USA has everything it needs to increase birth rates, it just doesn't prioritize that when immigration works just as well short term.