I feel lonely for my little people, because they rarely interact with one another. There's a small interaction when they marry, and another one when they make a baby, and that's about it.

I'd love to see the ability for two kids to play together or for adults to be able to do something (besides make a baby :D) together. One thing that both adults and kids can do, that's already in the game, and that's commonly done with someone else is play a board game. Give us a board game we can put on a table, where we can drop two or more family members on it. An adult playing with their kid, two adults playing, two kids playing -- you could get a lot of mileage out of just one thing.