These children are standing waist deep in cracks in the earth known as "Black Dirt".
This phenomenon occurs when this highly fertile soil goes through a long dry spell or drought.
Since this soil is nutrient rich with organic material it has a tendency to smell bad in the hot dry months.
Once wet weather returns, the cracks close up again.
These photos are courtesy of Mike L. in Texas.
To learn more about Black Dirt and the specific region it is named for visit here.