You don’t have to wait that long for this to become an issue. If your parents started having kids at 25, and you start at 25 (late by historical standards but a

You don’t have to wait that long for this to become an issue. If your parents started having kids at 25, and you start at 25 (late by historical standards but almost early by modern), they’re at least 50, probably even pushing 60 if it’s not the first of the first. Watching very young kids is hard on your back, lots of bending over and picking up. The raw strength required isn’t totally trivial. Even 50 year olds can have trouble with this. It gets better by the time they’re 2-3 and can walk, but of course other childcare options become more available at that point as well.