Hi, Alison! You are getting a bit behind the eight ball in terms of making your advanced dining reservations, but if you are willing to be flexible, I'm sure you'll find some dining experiences that will make your boys happy!
None of the restaurants "require" advanced dining reservations, but some restaurants are virtually impossible to get into without them. It would be a safe bet that getting an ADR at Cinderella's Royal Table might be a bit like hitting the lottery, but for a character meal experience the kids might enjoy, you could try for Tusker House at Animal Kindgom - an all you can eat buffet with Donald, Daisy and some of the gang. I know some people haven't had as much luck, but I can usually find something at the Crystal Palace - a Pooh and friends character meal - up until close to the last minute.
Other dining experiences they might enjoy are Whispering Canyon at the Wilderness Lodge - a favorite of my nephews at that age; and 50's Prime Time Cafe at Disney's Hollywood Studios. Also at Hollywood Studios is Sci-Fi Dine In, although those reservations are a little bit tougher to come by.
My kids have also really enjoyed the Benihana style dining at Teppan Edo in Japan at EPCOT, where they love watching the chefs work their magic. You might also try Rainforest Cafe at Animal Kingdom and at Downtown Disney, or the new T-Rex dinosaur restaurant at Downtown Disney.
If you can, get on the phone today! I'll stop talking now so you can go make those reservations. Oh, and to save you time in looking up the phone number, here it is - 1-407-939-9469.