I adopt children because it's easier to clean up the house and yard with more hands on deck. Kids are faster at getting wrappers to the trash, socks to the laundry, etc. More kids also means more cute things happening around the house.

I'm at a stage where I'm trying to get perfect career matches (congrats on yours, Salted8) and so I adopt a kid or two to make sure I have a new generation. In two of my families that's working out fine, they have plenty of coins. My third family has had worse luck. I think I may have to shelve the idea of a perfect match in that one and get a few high earners in there and concentrate on careers for a while.