CHICAGO — They may be a big hit at kids' birthday parties, but inflatable bounce houses can be dangerous, with the number of injuries soaring in recent years, a nationwide study found.

Kids often crowd into bounce houses, and jumping up and down can send other children flying into the air, too.

The numbers suggest 30 U.S. children a day are treated in emergency rooms for broken bones, sprains, cuts and concussions from bounce house accidents. Most involve children falling inside or out of the inflated playthings, and many children get hurt when they collide with other bouncing kids.