Personally, I think life's too short, and I have more stuff to do than work.
Its great that you have this position for yourself, which I do have as well, but that doesn't mean that everyone who is working harder shouldn't be rewarded for it.
But we currently have moved toward a cutthroat environment that often rewards those who work long hours, never take vacation, sick days, or other leave, etc. Is that really the working environment you prefer?
If those people do these sacrifices, and their overall performance actually does get better, then it should only be natural to reward them. Everything else would be unfair.
Currently, well-educated "career women" tend to have some of the lowest birthrates, likely because of the feedback factors you identify. They prioritize work to get ahead, and then either wait until it's too late to have kids, or only have one or whatever.
There are even many great men who didn't have children because they didn't have the time, Nikola Tesla is an example. But this is simply the deal you have to make, raising children takes time, such as doing work.
but there are actually good long-term social reasons to support parents, particularly those who are intelligent enough, educated enough, and responsible enough to do well at work.
I agree with the idea of helping such parents to raise children. However, this can be done e.g. by tax cuts if you have children / extra taxes if you have none. Why should the employer be part of the story? The employer the same benefit in an employee leaving to take care of their children than if that employee stayed home to watch TV or to drink in a bar.