The first thing that child needs to be taught is how to swim, those things are incredibly dangerous, pretty much any flotation device is unless you already are a swimmer. My parents never let me wear then until my dad taught me how to swim when I was 7-8 I think
My oldest son was picking up nickels in the deep end when he was 2. He started swimming at 15 months. Our other three were late to the swim game. They all were almost 2 when they learned.
Youngest of my Waterbabies... now all grown up!