Hi Lesa! The peeps can't go out the gate...Wish they could though. And once they leave for college they don't come back until you choose one of them to take over using the "New Generation" button that appears after one of the parents die...Then only the one you choose comes back to the house. The good thing is they get to keep all the upgrades you made with the parents. I hope this helps!
Hugs,
Lewanda