I spent 4 nights at the WL with 2 daughters (3 and 7). Although not an expert, here are some things we liked doing.
Get a water mouse and cruise around for 1/2 hour.
Ride the boat to FW (check out what river country looks like now) and to the Contemporary.
Get a list of clues from guest services about finding Hidden Mickeys.
Go for a bike ride.
Watch the fireworks from the boat dock in the evening.
Have dinner at Whispering Canyon and let the kids run around with the waiters and yell and scream.
The pool is nice, a tame slide, and lots of chairs.
Roaring Forks has good food for a quick bite, Artist Point looked nice but there wasn't enough time to plan a dinner there, and Whispering Canyon was wonderful.