My DS and DD (9 & 6 on our cruise earlier this year) are used to going to bed early and no matter when he goes to bed, DS always wakes up early. We tried to switch to the early seating once we got on board, but it just didn't work out. Naps were also out, though we did try to get in a quiet hour or so with a book.
All things considered, the late seating wasn't as bad as we had expected it to be. We would go to our room around 5:30 or so, order a PB&J or mac & cheese for the children plus an appetizer for the adults from room service, and shower and get changed for the early show and dinner.
On at least 3 nights (possibly 4) DS fell fast asleep on my shoulder in the dining room during the meal and didn't really eat anything. However, he didn't go hungry since he'd at least had a light meal earlier.
I'll admit that we've signed up for the early seating on our next cruise, and hopefully we've booked early enough to get it. But, I was really glad to find out that we could manage to make the late seating work out, too.
Have a great time!