Di, I am not making light of the insensitive questions you are asked, but I thought it might be a little consolation that the ignorant people are not just targeting the chlildless! I have 8 kids and here are some of the things people say to me:
Were they all planned?
Do they have the same father?
So is this it? Or are you having more?
Haven't you figure out what's causing it yet?
The last question is asked as a joke, but I want to say to these people, is it really your concern? Are you feeding them?
People just don't know how to be polite and sensitive anymore. If I didn't know you, I might ask "do you have children", never "how many??" I can't imagine being that presumptous. After hearing the answer "no" I'd go on and ask other things in an effort to get to know you. Each person is pricelss and special all on their own, marital and parental status do not make the person worthy or unworthy.