I was thinking of a case where the group goes through their old village in the course of the game, and suddenly who and what their family is actually has some bearing, something it wouldn't have generically had. But your situation with your daughter sounds similar.
I've seen GMs would absolutely insist on doing said filling in themselves, which seems weirdly overprotective of their authority over setting for something relatively minor (again, assuming you don't have a player who's trying to get some sort of serious advantage out of how they do that, but that's usually going to be pretty obvious).