That isn't realistic though, there will never be enough nannies for every family with children to have one.

If you wanted to pull a purely financial lever, you'd have to give couples enough money to offset one partner's income plus a lifetime of lost income due to the years spent outside of the job market.

IMO this would be perfectly fair and reasonable, considering they are raising a future lifelong taxpayer, but that kind of long term thinking is challenging.

That basically sounds like retirement. If you choose to stop working because of kids, you could be entitled to receive social security just like in old age.