Mei really fucking died is true?
No, it is not, must not be true lol. I think they were just trying to scare kids about taking adventuring too far...
Why the hell would a bunch of adult dudes at studio Ghibli,lead by a guy who thought a self-animated 3D zombie was a crime against humanity, say "hey lol let's fuck with everyone and kill off the little kid!"? No chance.
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When i was a kid i spent most of my summer holidays wandering around various cities. I render when i was the older daughter's age i was riding a second hand bike around a few neighbourhoods in Canberra, Australia, from Dawn til dusk. And climbing hundreds of trees...
That's what kids were meant to do in the 80s and 90s, 00s...... And like the whole time before then... Ever seen Stand By Me?
Contemporary parents, well i don't know where OP lives maybe it's a pretty scary place, but yeah once your kids are old enough to want to explore you would give them some slack... As i write this i want to walk it back a bit so I'll just say let your kids explore if you're in a place worth exploring/without much risk of crime.