Same boat. Don't want 'em. Ever. My family stopped bugging us a LONG time ago..
Co-workers and such that get nosey are fun though. You just have to develop some instant responses.
Q: "Why don't you and your wife have any kids?"
A: "Oh, we've had half a dozen or so. They fetch a pretty penny in Mexico!"
Smarmy remark: "You'll change your mind about having kids" * I get this one from male co-workers
Canned response:" Probably just like you changed your mind about sucking dick."
Q: "Why don't you want kids? Someday you'll be old and need someone to take care of you..."
A: "I hadn't thought of it that way! I guess the eventual cheap labor might be worthwhile..."
Q:"Who's gonna take care of you when you're in a old folk's home?"
A:" Your kids..."
See, all you have to have is a bit of a sense of humor. After all, they're being rude by pressing the issue and aren't entitled to anything more!
For random strangers I usually reply with a "Oh, God no!" delivered in the same manner as if I had been asked if I would like my testicles smashed with a hammer, when asked if I have any kids.
GT