In theory, it's supposed to balance out as women take on jobs that they wouldn't otherwise as a result of being able to share their childcaring duties. In practice, there's obviously all sorts of inefficiencies in the market to deal with - two people working part time might very well not net the same amount as one working full time and the other even less time. There's a number of issues to be solved, but that doesn't mean we should throw our hands up and say it's too hard.