Playground sand is unlike the sand found in hardware stores. It is known as safe sand, as it won't cause respiratory illnesses when inhaled. The kind of sand that you can buy sometimes has a California Proposition 65 label (or any other kind) warning of the health hazards contained within. These kinds contain harmful carcinogen (any substance capable of causing cancer) that will then become airborne and inhaled as children play. To avoid this, sand pits need to be covered and kept damp if possible. Thus if you plan on buying playground sand, look for silica-free sand as it contains no known hazardous elements. If you still don't trust sand after hearing all that, you can also just replace sand with something similar like rice or cornmeal. Even if it would then technically be considered food, please make sure your children don't eat it.
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