[iggldiggl]

It probably still holds on the level of the whole society. Modern society and division of labour means it doesn't have to be specifically your kids who care for your, but it still need to be somebody's kids. If nobody had kids any more, nobody would be left to provide any care, paid or not.

Plus it's not just about really literal full-on elderly care, but also simply keeping society running even when you're old enough that you can no longer actively contribute your share as much.