We should ask ourselves a question, if the system we're living in is not rewarding having kids, is a good system at all?
Many countries have tried giving every incentive possible. Cash bonuses, tax breaks, a year+ of mandatory child leave for both men and women, cheap child care, mandatory flexible hours, housing subsidies, cultural campaigns.
Some of them have a short term effect but none of them get the numbers up to replacement levels and the numbers keep going down.
It's hard to blame it on any one thing. Some might say "suburban car centric culture" but that doesn't explain Japan, Korea, Singapore, etc....
I can't personally imagine the numbers going back up.
If you want to see what culture will look like in a few hundred years, try and figure out what’s common between Mormons, Amish, and Muslims.
Those incentives are usually meaningless. Like 100€ monthly cash bonus. Could cover food, but nothing more. A year of child leave is good, but what to do during next 5 years untill you can put kids into the school system?
And don't forget massive opportunity costs. Instead of having a single kid, woman can have few more years of advancing in career. Instead of putting all time into one kid, woman can upskill, get a degree, etc.
And with second child it's three times harder.
Also turns out, many baby boomers are not eager to be present in life of their grandkids. If you pregnant - you are screwed. You and the father-to-be will take a massive hit in every aspect of life.
The are many programs like this all over the world; the issue with them is they don't give out enough money/resources to have a measurable positive effect - they should be much much more funded. Incidentally the biggest baby boom in my country (Slovakia) was during the largest buildout of cheap accomodation for young families in the history, also the maternity leave was increased to 3 years and there were various subsidies. So I think policies like that work if they are properly funded.