U.S. researchers are calling for a design overhaul of the inflatable bounce houses that are a staple of children’s parties after finding that as many as 31 children per day are injured while playing in them.

A study out of Ohio says that between 1995 and 2010 there was a 15-fold increase in the number of bounce house-related injuries in the United States, from fewer than 1,000 per year to nearly 11,000.

The increase in injuries was most pronounced in more recent years, with injury rates doubling between 2008 and 2010. In the last year of the study, as many as 31 U.S. children per day were treated for injuries sustained in a bounce house, or one child every 46 minutes.

Children can get injured when they fall out of the bounce house, or when they hit other children while playing inside.

The injuries included fractures, strains and sprains, and concussions, and most of them occurred either at a sports or recreation facility, or at a home.

"I was surprised by the number, especially by the rapid increase in the number of injuries," lead author Dr. Gary Smith, director of the Center for Injury Research and Policy at Nationwide Children's Hospital in Columbus, Ohio, told The Associated Press.

The findings were published Monday in the journal Pediatrics.

Researchers came to their conclusion after compiling data from 1990 to 2010, during which an estimated 64, 657 children under the age of 17 sustained a bounce house-related injury and had to be treated in an emergency department.

They found that the average age of injured children was 7.5, while more than three per cent of those injured had to be hospitalized or kept for observation.

The U.S. Consumer Product Safety Commission recommends that children under the age of six not be allowed to use full-size bounce houses. Smith said parents should keep children in that age group out of even the smaller bounce houses that are most commonly used at home.

Laura Woodburn, a spokesperson for the National Association of Amusement Ride Safety Officials, said recommendations for the safe use of bounce houses include not letting too many children in at one time, and not allowing younger, smaller children to bounce with older, bigger kids.

In an abstract accompanying the study, the researchers called for better guidelines for use, as well as changes to the design.

“This increase, along with similarities to trampoline-related injuries, underscores the need for guidelines for safer bouncer usage and improvements in bouncer design to prevent these injuries among children,” they wrote.

With files from The Associated Press