Don't want kids? You'll change your mind.

What do you think about people who tell women who say they don't want children that they will probably change their minds? I find both statements kinda annoying. On the one hand it's really not your place to give your opinion on a woman's life choices. On the other hand if you don't have the maturity to realise that you may change your mind later on down the line you don't really have the maturity to make that kind of decision. I still don't think that's an excuse to be rude though, how hard is it to just keep your mouth shut?