I haven't gotten through all of my interviews yet, but I also got asked a question about having / taking care of children. I noticed there was a discussion about similar questions earlier in this thread, so I thought I might offer my two cents about it. Personally, I found the question obnoxious and rude. Part of that is a response to the way my interviewer phrased the question ("When you have children in medical school, what will you do?"). Really, though, I think the question is incredibly presumptuous in and of itself. Without prior knowledge of my life, nobody would try to make assumptions about my interests or my talents; why is it okay to assume that I have definite plans to have children? Nobody can tell that information based solely upon a person's appearance.
Honestly, the tone of the question made me feel like my interviewer was trying to talk down to me. As a petite girl, I'm used to getting that sort of treatment (sometimes it's in a nice way, like when a guy offers to help me), and usually, it doesn't bother me--after all, it's normal for people to make assumptions based upon a person's appearance; I do it all the time, as everyone does. In the context of a medical school interview, though, I think it's inappropriate. All candidates should be treated as equals in the sense that interviewers shouldn't make assumptions about their personal lives.