If you're going to be in MGM, I think your kids might enjoy the humor at the 50's Prime Time cafe. We were there last spring and my kids (14, 12, 10 and 8 at the time) were hysterical because we had a very funny waiter. We went at lunch time, however, and that is less expensive than dinner. We are probably going at dinnertime this next trip. The food is not "special" here, the atmosphere is.
The California Grill was wonderful for the view and I loved the food, but my children had a hard time finding something they liked and it wasn't worth the money for them.
We all enjoyed the food at DTD's Wolf Gang Puck's cafe.
Crystal Palace breakfast was a great buffet with Pooh characters, but we did that many years ago.
Hoop Dee Doo Revue sounds like it would be good for you family, too, but I've never been; only read reviews here.
Coral Reef in Epcot is really neat with the huge window to watch the fish, but the children's portions are small. I loved the food, however.
The Garden Grill and Liberty Tree Tavern are both good for characters, but my family doesn't really like the food served family style, rather than ordering what they like.
I would look at the menus for each of these restaurants before making a decision and decide on the atmosphere you are looking for. (Also, each country in Epcot offers a unique dining experience).