My 2.5yo loved it, and has enjoyed a similar raft ride at our local water park since she was about 18 months old. It's just like a huge, long slide. The little ones sit with their legs straddling a strap on the floor of the raft and hang on to that, plus dh or I always put an arm around dd's shoulders, to keep her a little more secure.
My older dd, on the other hand, did not enjoy a similar ride at age 4, because occasionally the raft slid up the sides far enough to where she felt like she might fall out (never did, though). I don't recall Teamboat Springs' rafts going quite as high up along the sides, though. Also, she is a very cautious child and usually is the exception rather than the rule on this kind of thing. Just thought I'd mention it in case one of yours is on the cautious side.
Have fun!