I am building an eternal kingdom, and am trying to make it the most perfect and filled kingdom. I have all my sims have 4+ kids to fill the world with kids, and I'd like to fill the world with adults as well. I know certain quests will bring new characters into the world permanently. I've been planning on making a list of quests that will add people, but I'm wondering if someone has already done that?

It's not exactly what you asked for, but there are mods to populate your kingdom. Search for "Populous".