We just traveled in Septemeber with my 3 1/2 year old and 15 month old. I shipped everything to the hotel beforehand - so it was there when I arrived. I would definitely recommend shipping some bottles/sippy cups, diapers, swim diapers, a few juice boxes and lite snacks (raisins or the like) - just so if the lines are long and the kids need something immediately you have something available. It was great not having to have all that in the luggage - and I shipped disposables - so I could throw almost everything away after we were done and not have to lug everything back. Have a wonderful trip!
Oh - definitely bring formula too!