"They happen already grown up. Angels do too, for that matter. Although half-demons happen sometimes, mostly half-incubi and succubi, and those are born and be kids and grow up like regular humans."
"Well, it depends on what kind of demon, but mostly they're humans with maybe some extra powers and behavioral influences--a half succubus or incubus is less likely to think sex is a big deal, a half wrath demon would have a temper etcetera."
"And they don't go to Hell automatically or anything."
"People going to Hell who are evil is terrible and needs to be fixed, but if there were innocents going to Hell this would be a monumentally more urgent priority."
"Yeah. What happens with people who are bad but not Hell bad going to Heaven?"
"Like, they're still bad, just not super special bad, so how does it happen that they can't hurt anybody so Heaven will still be nice?"
"Well, things in Heaven aren't really breakable the way things on Earth are, and if you want to avoid someone then--Heaven doesn't really have a stable geometry the way Earth does, you can walk to places if you want but the way to do this is to start walking and intend to arrive there rather than memorizing a set of directions, and normally this works on people too but not if they don't want to see you. If you end up in the same place anyway they can sort of--metaphysically pretend they don't exist, and it works."
"What if people don't want to ignore someone but the someone is being mean?"
"Like, um," Mehitabel's limited life experience is not serving her very well here. "Like if they're family and they think they shouldn't ignore family but they're not being nice."
"Oh, yeah, stuff like that. Things sort of--rearrange themselves so accidental meetings that are going to go like that don't happen as often, but it turns out that you can't make absolutely everyone completely happy all the time without damaging free will."
"If succubi happened because people thought sex was bad did Hell happen because people thought punishment was good?"
"If we knew for sure it was that probably 'punishing people for the sake of it is bad' would have taken higher precedence over 'Hell exists and you really don't want to go there' in Scripture."
"Does it even work right if people are only okay to avoid going to Hell?"
"It would surprise me if there wasn't anyone who hadn't been scared straight by it, and also it was an opportunity to encourage people to be better rather than worse overall. Whether it did more harm than good or more good than harm in the long run is debatable."