For those ages I would say Animal Kingdom over Epcot and second would be MGM/Hollywood studios.
Animal kingdom has more rides and activites for their age groups and a whole "dig site" area to play around in. My son, 3, loves the safari ride! Its a bugs life 3-D show is a little scary for maybe teh 3 yr old, but the others will probably like it.
I used to work at MGM years ago and we live 10 minutes away from Disney