MGM
If you are at MGM for breakfast, we really like the ABC Commissary (sp?). It's not a character breakfast, but it has real breakfast food (eggs, bacon, sausage, potatoes, etc.) and we have always found it to be really good and served hot.
We like the brown derby for dinner. It's not cheap, but we thought the food was really good and very convenient if you are doing the Fantasmic Dinner Package.
EPCOT
We love Le Cellier for lunch at Epcot and I would think with kids, they would like that...good burgers, etc. Love the cheese soup.
If the kids are somewhat adventurous, we liked Yakatori, a counter service restaurant in Japan. They serve really good noodle dishes with beef & chicken and I remember it being pretty reasonable.
MK
We have eaten at Liberty Tree Tavern for lunch and thought it was very good. I had a really awesome salad with chicken.
Hope this helps.