Often it is just me and B in the car. We take Trev to school, to camp, somewhere, and then he and I hang out. When Trev first started school, B was always looking over at the empty car seat and asking "Where Trevor?". I would reassure him many times, that I hadn't lost or forgotten Trev.
Now Trev is going to summer camp 3 days a week. On Monday, B was VERY upset that he didn't get to stay and play with all the big kids. Today, B decided it wasn't such a big deal.... if Trevor wasn't going to stay in the car with us and go place, we'd use his car seat for someone (or thing) else important...
Note to all my car seat buddies: I'm sure by size and weight Elmo should still be rear-facing. I'll work on this and explain to B, so we don't have any Elmo injuries in the event of a crash! =P