I was going to ask the same thing, we have a 3 and 4 yr old but both are very good swimmers already, both can stay in the water without any floats. I see that there are some height restrictions on some things at the 2 parks, but other than that are there any things that young ones can't do?
We took two young children with us last year to TL (5 and 2) and they did okay. However, since they are good swimmers, I would recomend going to BB. The "wave pool" is definetly swimable, as the waves are only a slight bounce, unlike TL. Both have a children's area and are quite nice, as well as a lazy river. Enjoy your trip!
I've only gone to Typhoon Lagoon and the ketchakiddee creek area really, and truly exceeded expectations. My DH (who is sometimes also the oldest child ) really wanted to go and I went thinking it was a bad idea for a 2 1/2 year old and a 4 yr old and I was really very wrong!
The CM's do a good job at making sure the area only has small children, there are no deep area's, the slides have a foam floor. There is even a very small tube ride for the little one. The DD's had a ball with the geyser's and the water cannons.
Our kids (DD 4, DS 3) really liked BB last year (TL was closed the day we had slated for the water parks). One problem with the kiddie area is that it is impossible to help your kid get on to some of the slides and then get to (or even see) the bottom. It wasn't a huge problem on the slide that was their favorite b/c there was a CM at the bottom to help them out. But for a while the constant walking up and down was tiring. Once the kids got used to walking up to the top (including dragging a tube on that particular slide) and getting on by themselves, it was fine.