CASTLE ROCK, Wash. -- Police said a 3-year-old Longview boy died of head injuries after two adults fell on him at the Hoppin' Houses indoor playground in Castle Rock.

Jacob Pierce died Saturday at St. John Medical Center in Longview of a skull fracture.

Officer Jeff Gann said Jacob was at a birthday party for a relative at the play area, which features inflatable slides and obstacle courses. Jacob had either fallen off one of the inflatables or was standing beside one of them when two bouncing adults landed on top of him and they all fell to the concrete floor.

The Cowlitz County Coroner's Office ruled the death accidental but the boy's mother, Rebecca Pierce, said she couldn't believe it when the fun center continued with the next party.

“It's been an absolute shock. It’s a nightmare you'll never make up from,” said Pierce.

Pierce said the accident could have been prevented if there was more adult supervision on staff during parties.