Of course, it's ridiculous. Jzel, did the girls specifically ask you
why you didn't want kids, or was that information you added in connection with the simple question, "Do you have any?"
Not that it matters much.
It doesn't sound like you gave an
opinion, per se, as much as you simply stated why you have not chosen the same options they did and you gave your reasons. An
opinion would have been to say something like "I don't want kids because they demand too much money/responsibility, they suck the life out of you, they crack a marriage faster than a wrecking ball, etc." But it doesn't sound like you did that.
I have learned that giving your opinions at work is a touchy thing. You're right, you're entitled to
have those opinions, but you are not entitled to
voice them, per any standard HR department. Personal opinions, when voiced, can make people uncomfortable for whatever reason. If they happen to offend anyone (rightfully so or not), it's an HR issue. Wouldn't you say we all have the right to wear whatever perfume we want? Not so, if someone reports it's a distraction or an offense to them.

P.S. I've also learned that working daily with women can be a real pain in the ahhhss, because some of them are so insecure, jealous, catty or delight so much in starting trouble, and they tattle to whomever will listen.