My kids love the special programs they did in the lab (my kids are 9 now, they were 6 on our first cruise and we have gone on one per year since then, always on their birthdays---twins).
We like late seating because it is easier to find food around 6:00 (pizza and burgers on deck 9) to hold us over until 8:30 dinner. We also like ordering room service (now that I know it is free--we do tip the person who brings it to our room).
On a 3 day cruise, you just have to accept that you won't be able to do it all, so just try to do a little of everything. The ONLY time my girls made it to the pools on the ship was on the first day right after we boarded (they had swimsuits on under their clothes). That was also the only time the pools were not crowded (most had to wait for suitcases to be delivered to their rooms which is anywhere between 1:00 and 5:00 I believe).
I would suggest looking at the kids navigators at Barb and Tony's site:
http://www.castawayclub.com
and then picking the things they want to do. My girls had never done the kids programming at
Castaway Cay before, and this time they wanted to do the whale dig (it was the last year before they move to an older kids group and the 10-12 year old don't do the dig). They LOVED it! I am SO glad we let them do this.
The other thing my girls did not want to miss was the Friday morning Princess greeting. So those were the things we went knowing we wanted to do for sure.
After that, we had them go to the shows and dinner with us every night. Then we just sort of went with whatever we wanted to do after that.
You will have a great time, and you will come off saying that 3 days is not enough. BUT it's a start! Each time we go we try to do things we haven't done before. This time we tried out the treadmills in the spa and we visited the adult beach at Castaway Cay for the first time.
We already know that on the next cruise we want to try the banana boat rides!
Have a great trip!
DJ