Hi,
My kids are a bit older, 10 and 12, but I'll tell you what I found when we were there in December. First of all do look at /use a touring plan, either Unofficial Guide or TourGuide Mike or RideMax. But be flexible if you see it isn't working.
For the most part it worked great for us. The only problem we had was on the 1/2 day of the 1 plus 1/2 day plan for Magic Kingdom - it started off too slow and the kids needed action.
Epcot: Plan worked great, I went to get FP for Soarin' while DH took kids to Test Track, which they rode without FP twice and then went next door for Mission Space, also without FP. At this point they were happy and satisfied and the rest of the day was great.
MK: on the full day, sent DH for FP for Space Mountain while we went on Buzz Lightyear, then went to Space Mountain and rode it twice . As in Epcot, this made the kids so happy that all the rest of the day flowed.
Animal Kingdom:
Went straight to Expedition Everest and rode it (also x2 I think), then went to Kali River Rapids which was great fun! Then went and got a FP for the safari ride in Africa.
DHS: Don't know - sorry - DH was there with the kids not me, I went back to Epcot...
Basically, follow a plan and make sure to start the day with a big attraction!