That absolutely is not natural selection at all. Natural selection is the result of a random process. People deciding to have or not have kids is a conscious decision based on their life experiences.
Put another way, someone choosing to have kids isn't necessarily changing the balance between the child-bearing and child-free population in the world. If we could freeze the conditions that cause people to not want kids and keep them constant, we won't see the child-free "die out" and be replaced by people who only or predominantly want to have children. We'll just continue to see roughly the same proportion of people wanting and not wanting to have kids.
> People deciding to have or not have kids is a conscious decision based on their life experiences.
You're just looking at those who don't have children at all vs those who do, but that's not the whole story.
People don't decide these things in a vacuum - all over the western world statistics show that people have on average one child less than desired - mostly due to external pressures like availability of real estate and/or stable employment.
The environment simply doesn't support having more children, so those who do have them don't allow themselves to have more - much like animals which don't breed in captivity.
Countries like France largely staved off population decline because they decided to create an environment where people can have children as they naturally would.
Put another way, someone choosing to have kids isn't necessarily changing the balance between the child-bearing and child-free population in the world. If we could freeze the conditions that cause people to not want kids and keep them constant, we won't see the child-free "die out" and be replaced by people who only or predominantly want to have children. We'll just continue to see roughly the same proportion of people wanting and not wanting to have kids.