Rafi followed Sophie into her car seat before I could stop him; she was very gracious about sharing her space on the way to the park (and the treats I kept tossing in helped keep him from trying to climb back out while I was driving), but when he tried getting in with her again on the way home she made it clear that it was just a one-time thing... He went back into his crate in the way-back, and she curled up in her carseat for a much-needed post-park nap. :)