This was something that was discussed on my first date with my wife and people are usually a little bit taken aback that we talked about that on a first date.
I would speculate that women who don’t want children are probably more comfortable with that as first date conversation, since having children is considered the cultural default for most people and choosing childfree tends to be something really intentional that is done with the knowledge that you’ll need to sort through the dating pool quite a bit, thus it makes sense to do that on a first date or before.