Marl holes and the 'sinking sand' by the side of streams can indeed be dangerous. A young lad walking his horse in circles on such sand was swallowed up a few years ago here in a particularly tragic event when the circling caused the sand to spiral in a kind of land-based whirlpool.
I should imagine that the cultural effect of so much professional entertainment being provided has had the same awful result in children's games as it has in things like people whistling as they walk along, singing at work, etc, which are so forgotten now that people stare at you if you ever claim such a thing existed.