I just have a shorty wetsuit for my six year old. I bring his ski jacket, ski pants, light weight rain shell, windstopper fleece pants and jacket, ski gloves, ski mittens, a couple of hats and anything else that will keep them warm if I get caught in a storm. You can't have too much as I want a change of everything just in case someone falls in goofing off. I also have umbrella mounts on the raft for shade for them. I figure they could hunker down under a umbrella, low in the raft if it got real nasty too.
For your 2 year old, bring anything you can get to keep them warm. All I have is some fleece snowsuits and some snow jacket handme downs from my older son that I plan on useing on my 2 year old daughter when we do ruby this summer. Hopefully by then we will not need such cloths, but I will bring everything just in case. A warm tiny crew is a happy tiny crew!