Purely economically, only a total moron would have a child. Child labor has been outlawed and society says the (grown) child is their cash cow not yours, so the retirement from taxing the kid is spread across everyone else. Meanwhile you're asked to pay the lions share of the investment for everybody else to cash out on. So the name of the game is to let everybody else have the kids and free-ride the fuck out of that by paying some token contribution like the property tax for their grade school or whatever and then taking advantage of their tax dollars when you get older.

This is a huge departure from almost all of human history except the last 100 years in the developed world, where the family formerly was the safety net so these kind of investments and arrangements stayed in the family leaving a much stronger economic incentive for children.