Don't bother with any of the water parks with kids your ages. They will have just as much fun at the resort pool areas and you won't have to pay extra, nor pack all the "stuff" that is required for a day off site.
As a veteran traveling family at WDW, I would recommend:
Keep it simple. Don't make PSs for early morning if you kids are late sleepers. Don't OVERDO--there will always be other trips and as your children grow, you will add things and let things go.
Enjoy your resort and all it has to offer. You don't have to hurry and get to the Park to enjoy WDW. Take time to eat a good breakfast, use the pool, shop in the gift shop, etc.
Use fastpasses. That way, you know you will get on the attraction, and it allows you to walk around the park and catch some shows while waiting. Your kids will like the Country Bears Jamboree and the Tiki Room at MK.
Come armed with PSs for the special meals. You do not want to leave your mealtime to chance with small children.
This is my rule: do sit down meals .vs. counter service. If you price out the items, you'll find there's very little difference between eating off of china and having a linen napkin inside served than grabbing 3 seperate items off a cart and trying to slam them down while sitting on a curb! Okay, this may be a pet-peeve of mine, but I NEED to have some comfort and eating on the run something dripping off a stick just doesn't do it for me. Your kids will probably share one kids meal and you and DH can share an entree and an appetizer for a nice selection. My "kids" are now 15 and 17 and they wouldn't do it any other way.
Truly, it pays to enjoy your mealtimes.
Most of all, don't force the same schedule at WDW as you would at home. the kids will sleep when they're tired and eat when they are hungry. There is so much to look at and absorb that they may have more stamina the first few days than you think.
Have a wonderful time. It is our favorite family vacation spot!!
