alt Hacker News> My take on it is: you have to make your country/society a place where people will want to have children and feel/know that their children's lives will be good ones.
I think this is not the right explanation.
If you look say 500 years in the past, people definitely could not guarantee their children's lives would be good ones. In many (most?) cases, it was almost certain the children's lives would not be very good. Yet people had lots of kids.
Perhaps people just have better things to do these days than incessantly change the nappies, suffer from lack of sleep and time for basic self-care, constantly argue about how the cheese was cut the wrong way and whether we're watching another episode of paw patrol?
The poor have nothing to lose. It's the same around the world today, poor countries have high fertility. The OECD middle class has low fertility because they're worrying about other stuff (lost wages, career stagnation, etc). The rich (high fertility) have plenty of money for private schools, nannies, housekeepers, extracurriculars, etc for 14+ kids (Musk).
It's weird to say the poor are more secure than the middle class, but that's what the data shows. Opportunity cost is a real thing. If other middle class people forgo kids and you don't, house rents will go up and you might not be able to afford a place.