DS did the Storm Slides at TL when he was just about to turn 3, wearing a life jacket. We thought that he'd be frightened, so Dad went down first and waited for him in the landing area (on the deck, they don't let you wait in the water), while I sent him in at the top. He was fine and insisted on doing it at least a half-dozen times. You would be amazed at what some kids can do.
IMO, plenty of the "adult" attractions that don't have height requirements are fine for young kids with life-jackets, as long as they are not afraid of slides in general. However, in some cases the "kid" areas can have attractions that I think are iffy for kids who panic easily in the water: the two that come to mind are the ice floe and the t-bar at BB. Also, the lazy rivers can be a problem if they cannot be trusted to stay on the tube; if it is crowded and they end up in the water they can get trapped under other peoples' tubes.
When it comes to toddlers, I like BB better.