I'd like the idea of an 1800 theme.
I was thinking about a world where there are multiple gateways to other worlds. Or maybe the world that humans live in is just the space between worlds with many ways to travel from one to another, but all forbidden to humans, usually sealed to demons and somewhat 'claimed' by angels or another race if you'd want to add that. But they can live with it and they don't feel the urge to explore. Everyone disobeying those rules is an enemy of whatever they live in. So that would make the child an 'outlaw'ish person'.
This is just an idea. Not sure what to think of it myself.
When I think of worlds I usually think of Avatar, Lord of the Rings/ Hobbit or Narnia xD With all kind of creatures and floating rocks.. I'm really bad at this.
i was wondering. When the demon takes the kid with him, where does he want to take him. Back to hell would be a horrible idea and would be certain death for the child.