The two were alone in the car when the 4-year-old found Brayden's mother's unsecured gun and discharged it, fatally striking Brayden, the sheriff's office said.
The first count of attempting to assassinate the president carries a maximum sentence of life in prison if convicted.
The Secret Service Presidential protection mission dates back to 1901; it was formalized after the assassination of President William McKinley.
California Attorney General Rob Bonta on Tuesday highlighted what he called historic progress in the state's fight against gun violence.
New video shows the moment an Oklahoma high school principal tackled an armed former student in the school's lobby before being shot.
The Los Angeles Police Commission has determined that members of the LAPD acted improperly during a shooting involving the former wife of Weezer bass player Scott Shriner.