Wow, that's a loaded question. I would say not to miss as much as possible. How long are you staying? What resort? Check out Expedition everest, it is a great ride. You can do child swap for anything the 4 year old is to small for. Don't miss wishes, Iluminations, or Fantasmic. It is a wonderful show. Try for the second showing of Fantasmic, it is usually less crowded. Everything in the Magic Kingdom is worth doing. Mickey's Philarmagic is great. Epcot requires a lot of walking, but well worth it. MGM, don't miss the stunt show since you have boys, Tower of Terror is they are not to scared, and Rock n Roller coaster is awesome!!!! The week after Christmas is extremely crowded, so take advantage of early entry and late nights.
I go to Disney twice a year and own DVC. So much to tell you, so little time. Don't expect to get into a sit-down restaurant if you haven't made advance reservations, they will more than likely turn you away at the door. If you have any other questions, let me know!
Some favorite:
Test Track, Missin Space, Spaceship Earth, Turtle Talk with Crush,Illuminations (Epcot)
Tower of Terror, Rock n Roller Coaster, the Osborne Lights, Indiana Jones, Stunt Show, Beauty and the Beast stage show, Fantasmic (MGM)
Expedition Everest, The Lion King show, the new Finding Nemo show (get there early, Safari, Dinosaur (don't go if 4 year old doesn't like dark places) Kali River Rapids, It's tough to be a bug(Animal Kingdom)
I can't say there is to much not good in MK, so try and do as much as you can. DOn't miss Big Thunder, Splash Mountain, Space Mountain, Mickey's Philarmagic, Pirates, Wishes, all the parades especially Spectomagic, Haunted Mansion