The ones who leave their jobs to take care of their kids. ***Every case is different, there are situations in some families when the best solution is not to have both parents working full time, in that case ignore my further comments.
I have a problem with the assumption that only moms have to leave their job for taking care of kids, it could be men too, why not? Only moms go on six-month maternity leave. Why? All companies need to revise their paternity leave policy. It HAS to be equal. From what I hear Microsoft and Amazon do have (about) equal maternity and paternity leaves.
You could tell yourself that your kids will be better off cared for only by you, but there is no research that bears that out, and while there are times that intense parental engagement is needed, working parents are able to achieve that, too. It is a myth that only stay-at-home moms take the best care of their kids or have the time to instill the right values. I have seen brilliant achievers even though they have had both their parents working. Although one may think that for any individual woman staying at home might lead to less stress, more happiness, and a better situation for her family, studies confirm that there is more boredom and depression.