I speak from experience. All the friends I've had who've become the victims of childbirth turned into completely different people that I didn't like anymore. I don't blame them for wanting kids, and I don't necessarily think you have to become a completely different person after popping out a few, but the fact remains that almost everyone does. I suddenly had nothing in common with these friends anymore, and though I tried to continue the friendship, there was nothing there. Meetings became awkward and the friendships just naturally failed, as much on my end as on their end. Julia will tell you the same thing. Suddenly the fact that she doesn't have kids and doesn't plan to becomes this huge gulf between she and friends who have kids, and they begin to have nothing to say to her because their whole world is wrapped up in the tyke. I've had friends who had major changes in circumstances in a variety of flavors, but in my experience, nothing kills friendship like children.
It should also be noted that it's completely different if you meet someone who already has kids, because then they're done changing, so you already know what you're going to get. I'm talking specifically about friends who have no kids making the transition.
EDIT - Some people have told me this is because I'm just a big child myself who does nothing but play videogames and live in fantasy worlds, which some may be tempted to suggest here despite likely sharing the same affliction at least to some degree. But I'd then have to remind them that I probably work more than they do, that I spend a great deal of my free time taking care of my disabled wife, and have hobbies ranging from classic literature to reproduction historic maps to philosophy. It isn't that people just stop doing things they once loved to do (this has happened in every circumstance), usually fun things like games or cars or what have you, and it isn't just the fact that they often become more responsible people. You don't need to have kids for that to happen, and I've never seen that as anything but positive when it happens in other circumstances. Really, I don't know exactly what it is, I only know that it turns good people into Wal-Mart shoppers.
