Attached is a good video from the American Canoe Association ACA about ensuring safety for children when paddling.
My take: kids AND adults should always wear PFD’s when paddling. A PFD that fits and is worn properly is your best bet if you tip over in a strong current, get stuck in a strainer or hit your head falling off of a SUP (Stand Up Paddle Board). Unfortunately, people die needlessly every year in water sports. I check the news each time there is a death in a nearby river and can not remember a person wearing a properly secured PFD being the victim. Be smart, always wear a PFD.
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https://www.youtube.com/watch?v=t_t6fF74lbs&feature=youtu.be