Three children were injured by shrapnel after a fellow elementary-school student pulled the trigger of an assault rifle mounted on a police motorcycle during a school assembly, authorities said.
The AR-15 was locked to the side of the motorcycle that was on display at Newman Elementary School on Wednesday during an anti-drug programme when a student managed to fire it, Chino police spokeswoman Tamrin Olden said.
"The bullet disintegrated when discharged by striking a metal plate where the barrel rests against the weapons mount, and metal debris apparently struck some children and caused minor injuries," she said.
"It is likely that metal debris struck two children resulting in extremely minor injuries," Olden said, adding that the children were treated at a hospital and released.
A third student was examined at the school and released to parents, she said.
The children were treated for cuts and scrapes, said Fire Department spokeswoman Massiel Ladron De Guevara.