Hi Melissa!
Thanks for your question. I took my son to both water parks when he was about 2 years old, and he seemed to thoroughly enjoy both!
I would caution getting on some of the larger slides with a young one. However, Disney considers all ages at each water park. For instance, at
Disney's Typhoon Lagoon Water Park, there is an area specific to preschoolers called
Ketchakiddee Creek. Here, they have size-appropriate mini slides, as well as a number of water activities my son thoroughly enjoyed (he spent a couple hours here alone). There is also the
Storm Slide, which I slid down with my son. It has small drops and you end up in a shallow pool. Each kid is different, however, so use your best judgement as to what you feel your child can handle and wouldn't be fearful of.
Disney's Blizzard Beach Water Park has an area similar to Ketchakiddee Creek named Tike's Peak, another water attraction that caters to preschool-aged children.
So, using my son as an example, he certainly enjoyed himself at both water parks at that age. Plus, there's always something about playing in the water that puts a child soundly asleep afterwards, a benefit for Mom and Dad. :-)
Thanks again, and have a splashing good time if you decide to go!
Terry