One of the biggest issues facing people who want to have kids today is that they are a major expense. Even for those wannabe moms or dads who aren't interested in private schools or the latest baby gadgets have to think long and hard about how to budget for children. That is a whole other person or several who isn't going to be increasing the family income themselves.
As a result, most of those who want to have kids have to make sacrifices here and there to be able to afford them. Perhaps they don't take as many vacations, or they switch up where they buy their groceries.
One of the most common ways in which parents try to afford their children is that they go back to work as soon as possible. It isn't necessarily the best solution, but many families simply have no choice. There may be value in having a parent at home when the kids are young, but these days, it often isn't feasible to survive on a single income. Getting into debt when there are children to pay for is a lot worse than only having to think about your own finances.