When you think about backyard safety, you probably think about swing sets and baseball bats—not sandboxes. But sandboxes that are dirty or contaminated can be harmful to your children. In fact, the National Sanitation Foundation International swabbed 26 different public places and found the playground sandbox contained the highest level of bacteria.

The American Academy of Pediatrics suggests the following tips for keeping your sandbox safe:

• Always keep your sandbox covered when not being used, to repel insects and animals that may choose to hide out inside.

• When the sand is wet, allow it to dry before you cover it, to prevent the growth of bacteria.

• Frequently rake the sand to get rid of debris.

• Never allow pets to play in the sandbox—they may confuse it with a litter box.

If your sandbox hasn’t seen any use since last year, it’s also best to replace the sand with a fresh batch. To get rid of your old sand, you can use it in your yard to fill in areas that need to be leveled. Otherwise, contact your local waste management organization to get advice on how to properly dispose of it.

Finally, you work hard to keep your kids safe. So think twice about letting your children play in sandboxes that are left uncovered—like on public playgrounds—where potential hazards can be lurking.