From Matt Yglesias:
Family life is subject to a vicious economic conundrum known as Baumol’s cost disease. Economy-wide wages are linked to economy-wide productivity. That means that over time sectors of the economy that don’t feature productivity gains will see rapidly rising costs…
Child-rearing is basically stick stuck in a kind of dark ages of artisanal production, but as market wages have risen the opportunity cost of this extremely labor intensive line of work has steadily increased. The implication is that societies that want to continue existing in the future are increasingly going to have to find ways to subsidize parental investment in the next generation.