Make sure that they KNOW they cannot see all of WDW in one trip.
Make sure they do NOT try to see all of WDW in one trip.
Slow down. Enjoy the details. Let the KIDS decide what to see. Go with the flow.
Have them make a LONG list of things they would like to do and see. A list SOOOO long that they know they cannot possibly see or do it all. The biggest mistake people make is trying to do too much and forget to have FUN!
If the kids are Star Wars fans they should try to get picked for Jedi Training at HS.
Get to Tom Sawyers Island when it first opens and try to find a paint brush to get FP's to a ride in MK. Lots of people know about this so it is a contest.
The Kim Possible "game" at EPCOT is supposed to be fun. We tried to do it last trip but the kids got sick and it was a no go.
Certainly they have to try Club Cool for the sodas at EPCOT. Make sure the parents know about the Beverly so they can watch the kids if the kids try it.
Our kids love going to Simba's Clubhouse. Good break for them and us.

Our kids are in the same age range and the oldest is not sure if she wants to spend much time at Simba's anymore. I assume the Poly has a kids place like AKL.
The Pool. The Pool. The Pool.

Do kids every tire of the pool.
We took our kids to ride the pony at Ft. Wilderness when they were younger. There is a weight limit for the ponies. I don't know if they have a horse ride over there or not. The boat ride over to Ft. Wilderness is very nice. And they might like the Hoop Dee Doo Review.
There is a Pirate Cruise the kids might like as well. We might try that this trip.
If the girl has ear rings you can pick an Oyster or two at Japan in EPCOT to get pearls which can be made into jewelry. I think there is a place in DTD that does something similar.
Later,
Dan