When we went last summer, my kids were 7 and 10. I planned mid-day breaks at the hotel all week. Turns out, DH and I would use those breaks to rest, and the kids, no matter how hot and tired they were when they left the park, would be bouncing off the walls of our little hotel room as soon as they got in air conditioning for a few minutes
Our hotel breaks got shorter and shorter as the week wore on. I finally realized that a nice long lunch in a park restaurant would have served the same purpose and saved some travel time and probably a few frayed nerves.
Another advantage of going back to the room, though, is replentishing supplies (water bottles, snacks, etc.) or even changing out of wet socks (it was pretty rainy). Also, since we were there during the busy time, there was not much point being in the parks mid-day due to the crowds.
If I were to do it again--I would make more PS's for late afternoons and stay around the park. Or maybe hop a bus or a monorail to go to another park.
At that age, my kids really could handle a 7am-11pm touring schedule as long as there was some change of scenery and a nice long meal in there somewhere.