Aye, but children are expensive to raise everywhere, and the less affluent often end up short on schooling, health care, and the assorted modern toys people nowadays take for granted. We went from one tv in the living room to one in every room in the space of a generation, one house phone to a cell in every pocket, one car to his & hers SUVs because people have really fat asses or something. I dunno, I could never figure that one out. No one buys THAT much at Costcos. Usually.
Besides contributing to the house functions as well as economy, mortality rate is also another factor, as traditionally survival rates were literally 50:50. In affluent societies, increased survival rates means 'backups' are no longer necessary.
Then there's also greed. People like money, and once they can access a nice flow of it, want ever more. Having less children means less waste on the distracting buggers, more money in the account.
I disagree on student debt though, as it is a choice. If they choose schools with higher tuition and degrees with lesser returns moneywise in the long run, that's on them. *old man voice* Back in my day, kids had jobs when they went to college. Ok, at one school I went to, Hunter (CUNY) it was more the trend; Fordham U later (big mistake, ugh, what a waste) which is loaded with entitled suburbanites, not as much, and those that did work tended to be local commuters as opposed to those who dormed who worked at improving their beer pong skills.
Nowadays kids are well into their 20s without having had their first job yet. Plus we had to hear about how our folks struggled simply to acquire books or even clothing. No fancy excess accroutrements for that lot.
But we are running room, costs are rising. Even keeping a house years later can prove unaffordable. Two on my block who bought their homes in the 1970s - paid in full in cash, no less, due to being 'privately employed entrepreneurs' in the, um, grey market sector, can't keep up with the upkeep and taxes in their senior years, even with middle aged offspring still residing at home (or partially because of it, as I suspect with one dingbat that used to live down the block). So now they have to sell.