Won't the kids wake up when you get back anyways to brush their teeth? I would just get them dressed in jammies then, because I'm a germaphobe! Wouldn't want them riding rides, and walking around etc in jammies and then putting them into bed in the same clothes.
I always got them ready for bed at the parks. But I did it just as we were leaving- we didn't walk around any further after changing, and they rode in the stroller and didn't walk around. My kids always, without fail, passed out in their stroller on the walk back to the hotel, so I liked to have them ready rather than wake them up. I brought tooth brushes, too. The baby care center is great for this, but it closes right on the button of park closing, so just keep that in mind. Whatever works for your family, I say!