I mean, it can be offset with money. - Kids take time - Yes, so does working. If you cutout the 90h my partner and I spend working, that's a lot of time to put into raising children. - Kids take effort - Yes, so does working. If I didn't need to work this becomes much easier. - Opportunity cost - Yes, just pay me for the opportunity cost. Pay for my PhD after my kids are in grade school.

It's just that these policies are very expensive, and right now we allocate our money mostly to make rich people richer and maintain very high QoL for our elderly population. That's a choice we make in setting up our society.

Exiting the workforce for a decade (Replacement fertility rate is 2.1 implying some people will have 3 kids, spaced 2 years apart plus 5 years of child-rearing until kindergarten) has an opportunity cost that is potentially in the millions of dollars, depending on the industry, and the time costs of child rearing doesn't suddenly end at 5 either.