With us, it's about 13sqm for the bedroom, 8sqm for the dressing room, and 2x children's rooms of 19sqm each – that's how it turned out based on the floor plan, originally 15sqm was planned for the children's rooms. The argumentation is like with most here: parents only sleep there, children's rooms are also for staying in, although I find the argument about space requirements for children over 14 years only partially suitable. They shouldn't just hang around at home but socialize, meaning doing sports and/or activities with friends.
If they want to study, I will advise them to get a shared flat room at the start of their studies, because that's where you learn for life, and especially the very "wild" time during studies as a home sleeper?! No thanks, I want to spare them that experience. Of course, they are always welcome at home and of course living at home is always an option. Independence is probably better promoted during that phase through their own shared flat room/their own apartment... so we actually wouldn't need the 19sqm children's rooms – but they don't bother either [emoji6].