I've said it before, and I'll say it again: the only way to get them to stop is by being as crude and shocking as possible. For instance, a cousin once asked me when I was going to have kids, and I replied with a straight face, "When the world runs out of wire hangers." Note how I said "ONCE." She never asked again. People tend not to bring things up if they are afraid of what you are going to say.

Granted, this may not be an appropriate thing to say to a boss or coworker, but family? I'm really not concerned with what they think of me.
As for the baby talk, it doesn't bother me as much I guess. I use it as an opportunity to talk about my cats. If I have to hear about your human baby, then you have to listen to the story about how my cat spent 5 minutes trying to get a piece of tape off her back foot. And, yes, I'm going to personally demonstrate how she shook back foot and walked in circles trying to catch it. If they don't like cats, oh well.
-D.