It could be because danger isn't experienced as a part of childhood.
True, children were killed accidentlally during horseplay, as well as suffering crippling injuries. No one really wants to return to that.
I do wonder, though, whether reluctance to let a child climb a tree without a helmet and joint pads robs children of the experience of danger out in the open, in a less sneaky and more wholesome way. If a 12-year-old child would seek a danger high through the perverse means of the choking game, which really has more than a touch of sexual masochism about it, maybe he should have been jumping off the high board at the pool years ago.