From Kite night.
We went to the excellent UFO in Weston and, after Douggy's excellent advice, splashed out on two kites. The first is a two-line stunt kite, the Cross Air 1.5, which B found was stable to fly but also responsive enough to develop steering skills for cool tricks. Crucially, it has no hard parts and doesn't break when it crashes. We also got a single-line delta kite for £10 that was very stable in the air and which C got to grips with very quickly.
We spent two happy hours flying them in a field near where we live that has recently been cut for grass. It is a wide open space with no hazards around, but with a gentle slope. We flew the kites lower down the slope, which faced into the wind. It felt like there were rising air currents without too much turbulence, but maybe the kites were stable because they were good and they didn't need much wind.