I went to buy one and people talked me out of it. I may have tried to get one for my daughter who was to young at 3. All of them are more for 12+ year olds.
My idea was this though, what do people do who sail around the world with young children for safety? Sort of funny because I do not think it is addressed much. I just wanted one for my 3 year old daughter at the time as even though I have a raft you are still exposed to the weather. They said in that situation just get a TPA (thermal protective aid)
I'd be curious what other people have done in this situation.
Mind you, because of what I do for a living, I keep everything to the max, including safety. At some point your back will be against the wall and everything comes in handy there!