I think I'd skip AK and do MGM instead.
At AK, your kids are too short for Expedition Everest, Dinosaur, Primeval Whirl, and I think maybe even Kali River Rapids, which isn't all that fun to me and drenches you. Tough to Be a Bug terrifies my kids. That leaves the Triceratop Spin, which is Dumbo w/dinosaurs instead of elephants, the Boneyard playground and the animal exhibits, which are great, but even though their commercial says it's "notazoo," well, it's a zoo. The Pocahontas show is OK and the bird show is good, but again, you can probably see a bird show at the zoo. The Lion King show is amazing, but not worth missing Fantasmic for.
At MGM, the only rides your kids are too short for are Rock and Roller Coaster, Tower of Terror, and maybe Star Tours. There's Playhouse Disney that they are the perfect ages for. There's also a parade. And you can meet Buzz and Woody.
Also, depending on when you're going and whether you really want to eat at the restaurant, we didn't find the Fantasmic dinner package to be worth it for us. So you might also consider skipping the dinner package and using that money to buy hoppers.