Hi Paula,
The water parks are a great way to spend some time out of the main parks and have some fun in the water. My family always plans a day at the water park when we are there in the summer.
Because your children are younger, I would recommend
Blizzard Beach. The wave pool, Melt-Away Bay, is large and much milder than at Typhoon Lagoon. Plus you can have a tube in the wave pool which is fun.
There are also more family rides that you can go with your children. Teamboat Springs is a family favorite for all ages. Cross Country Creek is a lazy river to spend the time traveling around the park.
The best is the children areas for the little ones. Tike's Peak is perfect for children under 48 inches. Here they can play and splash on slides and water areas designed especially for them.
Wishing you a magical vacation!
Beth