Aquatica has two separate areas designed for the younger guests. There is a LARGE interactive play area, found here:
There is also a smaller toddler area, which would probably be the best fit for your youngest two:
If they enjoy playing in the sand, there's a great sand beach that spans the area where the two zero entry wave pools are:
And you could also float the along with Mom and Dad on the lazy river
or in Roa's Rapids.
Just be sure to use lifejackets, even for the adults. A word of caution about Roa's........the current is very brisk, and a child could be swept away from you very quickly if you are not careful. So be sure to have a good, firm grasp of baby before you get going, and this is one place you wouldn't want one adult to take two babies at once. Otherwise, the wee ones will probably have a ball and find Roa's to be a real thrill!
I can't speak for the babies, but my kids LOVED Aquatica, and so did we. We have been to the Disney water parks, Camelbeach in PA, Six Flags in NJ, Great Wolf Lodge, and Sesame Place when they were little. Everyone really had a great time at Aquatica, especially Roa's. It's so much fun! I wore a life jacket, even though I can swim, just because it made me feel very safe. It's fast.