Usually the big kids are the ones who get to paddle the tandem kayak. At our picnic at the beach yesterday, though, we had brought the inflatable winter sled to use in the water. It went from being a shallow water floatie toy to an expedition kayak for a five-year-old pretty quickly. Paddling it with the kayak paddle involved doing the twist with your lower body, as the 'coracle' swivelled almost 90 degrees with every stroke. Fiona got the knack of it very quickly though, and had a riot scooting around like a floating bumper car.
The lake is much warmer now. Even I got in for a swim fairly easily.