According to Sioux Falls police Chief Doug Barthel, the boy had gone into the several-feet-high foam often generated there by the river, and perhaps into the water itself.

CNN: March 16, 2013 -- Updated 0041 GMT (0841 HKT)

It's made of steel, concrete and high-density foam.

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To address safety concerns, the play areas are usually surrounded by a 4-foot-high wall, with foam-padded floors and only one exit.

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