I offered a distraught 3½-year-old milk this evening, and she accepted, and she got nowt when she tried. Could be the pregnancy, could be her latch, which was getting worse and worse before. I know that Eldest just gradually lost her latch and couldn't do it, and that was that.
It had been a couple of weeks at least since the last time, too.
It's a slow process, weaning off.