What do batteries, coins, jewelry and toys have in common? They’re all found in your house, and they’re all commonly swallowed by young kids. According to a study recently published in the journal Pediatrics, the number of young children under age 6 who have visited an emergency room because they swallowed foreign objects has nearly doubled in the last 20 years.

The researchers analyzed data from the National Electronic Injury Surveillance System, which tracks consumer product-related injuries in the United States. The researchers estimated nearly 800,000 children were treated in the ER for swallowing foreign objects from 1995 to 2015. In 1995, there were about 9 cases per 10,000 children. In 2015, this rate had doubled.

More than half the children involved were boys. The most commonly swallowed items were coins — specifically pennies — followed by toys, jewelry and batteries. While 90 percent of the children were sent home without being hospitalized, some were seriously injured. In rare cases, some died.

What can parents do to keep their kids safe? They can choose age-appropriate toys and follow the manufacturer’s instructions for proper assembly. Parents can also store items like magnets and batteries away from where kids can easily reach. Safe Kids Worldwide, a nonprofit organization dedicated to protecting kids from injuries, suggests parents try to literally see the world from their child’s point of view by crouching on the ground to see what small objects can be viewed from a child’s eye level.

If you think your child may have swallowed a foreign object, call your pediatrician or go to your local emergency room immediately.