Bouyancy aid on the Meridian

I was interested to see that this life belt on Scilly is given a weight in Newtons. It is 100N but is suitable for people over 18kg. Such a person would have a weight of 180N so 100N must refer to the ring itself. It must have a mass of 10kg. I wonder whether the child having to be over 18kg is really about being big enough to grab the sides of the ring.