My 10 year old grand daughter has taken two years of classes in prams and loves it.Wish we would have started her earlier. Every child has different interests and timing.
Look at the picture on Victoria's website. Those are life jackets on every kid and the law usually requires children to wear them whether sailing or power. My grand daughter knows that if we are on a boat, power or sail, that she wears a life jacket. Get your child comfortable with the water and don't let the fear of the parents get in their way. Teach respect of the water and never fear.
All that being said, I would invest in a good, COMFORTABLE, life jacket. Just as with adults, if it is not comfortable they will not want to wear it.Some of those jackets in the picture are very uncomftable looking.