Whatever you think about the question, apart from the fact that it's unlawful to ask, it's incredibly douchey. It's none of your business, and implies that you think the woman is going to be a complicated hire because she's got kids.
In case it wasn't clear enough, the idea isn't that the interviewers are concerned for the kids. They're not. They just think they can predict the absentee rate for people by their chromosomes. Women with kids have to stay home when the kids get sick, right?