Most matches answer "Not at this time." It would be better for them just to leave it blank, which I think means the question is not even displayed with the profile.

This is the place to pass along any important details about yourself that haven't been brought up yet. I believe that any previous marital status and children (if any) belong here. As do any strong deal breaking requirements you may have. But think long and hard about insisting on anything, and express it as positively as you can.