We are using climbing harnesses (Edelrid Fraggle) rather than sailing-specific harnesses. The Crewsaver child harness has no crotch strap and the West Marine child harness does not look that strong (it looks like it has no D-ring, tho I never went to see it in person). Also, I just want something to keep them from falling off and will be watching them so I do not expect to be dragging them behind as a sailing harness is designed to do. Plus the harnesses will be fun in their tree fort. For a tether I am using a continuous loop of spectra webbing, cow-hitched to the harness, that provides 45" of tether. They will attach to lifelines with a carabiner that has a safety latch so that it requires two hands to open it.