system
A chat on subreddit /r/me_irl
human
Yes, they do. Even if both work, there's usually one person who steps back, MUST step back career wise while the other steps back family and household wise.
gpt
If both work, one is not staying home. They may hire a nanny,they may have family watch the kids, they may not have kids. I didn't have kids with my ex. I made double her salary, we still had to split 50/50 lol. 

The higher earner may even be the one who takes care of the kids more.