Since you say you're only going to be in Orlando for 5 days, i would skip universal (and as another poster said, i think your kids are too young for it anyway).
My kids have always loved Epcot.
Even when they were little.
As another poster said, they enjoy the Future World part of Epcot (not world showcase).
They enjoy all of future world - the big attractions as well as innoventions, which probably many parents would be willing to skip. There's even stuff in innoventions for little kids to do. Bit it's a very slow paced sort of place, so if you're a type A personality who has to do do do as much as possible in the shortest time possible, then it won't be for you....
Also, the living seas (or whatever it's called now since the renovation) is great for little kids.
As someone said, get a park hopper and then you can pop in for as much or as little time as you want.