One of my favorite childhood toys is making a comeback—the hula hoop. My friend Suzi and I spent hours on the front lawn perfecting our technique and competing to see which of us could keep a hoop circling our waist longer. This year I relived that part of my childhood. While sitting in a park, I watched as children of all ages and sizes tried their hardest to keep hula hoops from falling to the ground. They twisted and turned with all their strength, but despite their exertion the hoops landed on the ground. Then a young woman picked up…