If I were bringing four children of that age on my cruise, I would make sure that I brought a good supply of booze for my nerves.
Just kidding about that. My wife and I took all three of our girls (11, 6 and 3 at that time) on a seven night western caribbean out of Galveston last December and they had the time of their lives. They nagged us constantly to go to the Adventure Ocean facility. THEY WILL LOVE IT!!!