Mainly an issue with feminism being widespread but living/working conditions not having caught up with it. Society is set up assuming that the wife will stay home to care for the kids. As a result having children pretty much requires either enough disposable income to outsource caring for the kids (nanny, extracurricular activities, etc), or one of the parents staying at home.
For conservatives it's less of a problem because it's more accepted to have the wife stay home.
If we want birthrates to raise again we're going to have to figure out how to make having kids not be a stopper for your career.