A 7-year-old boy fatally shot his 2-year-old brother after finding a gun in the glove box, according to authorities in California.

The shooting unfolded just before 4 p.m. Monday in the cab of a truck that was in a parking lot in Rancho Cucamonga, the San Bernardino County Sheriff’s Department said.

The shooting appeared to be accidental, sheriff’s department spokesperson Gloria Huerta told ABC News.

The boys’ mom had just parked at a shopping center and was outside of the car, unloading items to bring inside, at the time of the shooting, Huerta told Los Angeles ABC station KABC.

The investigation is ongoing; once completed, a report will be sent to the district attorney’s office for review, the sheriff’s department said.

The type of gun and its registration information have not been released.

“Gun safety is a huge responsibility, but it is also a moral obligation that we have to our children,” Huerta told KABC.

Hundreds of children in the U.S. unintentionally shoot themselves or someone else every year, according to the nonprofit Everytown for Gun Safety.

Last year, there were 411 accidental shootings by children — the highest number Everytown for Gun Safety had seen since it began tracking the incidents in 2015.

So far this year, there have been at least 270 unintentional shootings by children, causing at least 99 deaths, according to the organization.