expensive real estate is already working as a child tax. you want to raise kids - you need a bigger house, and with prices skyrocketing fewer and fewer parents are able to afford a child
Niger has the highest fertility rate in the world[1]. As far as I know, they don't live in palatial affordable mansions there. How are they managing to afford all those children?
[1] https://worldpopulationreview.com/country-rankings/total-fer...