I really don't know why I am posting , after all my advise is to skip it.
We took my daughter when she was 9 months old to WDW and skipped the water parks this year. We stayed at Poly and the pool there was more then enough for us at that time. I love TL and BB, but I knew that we just couldn't enjoy anything and it is too hard to keep them out of the sun. If you use a resort pool, then you can head back to the room to take a nap, dry off, eat, clam down, get something you forgot.
We didn't really miss the water parks, we had been before, when we weren't parents. It really depends on how much it means to you. A fun pool would be easier and just a great for the kid. My daugther really liked crawling around at Poly pool. Y&B has as great pool for kids and CS is good too.
So my advise it to waite. I don't know long, I wonder myself when a good age is to take them, 3 or 4? Have a great trip.