A 4-year-old boy was fatally shot by his 6-year-old brother in East Orange, N.J., on Saturday, the authorities said.

The older boy was playing with his mother’s gun at the family’s third-floor apartment on Norman Street when he accidentally shot his brother in the head shortly after 11 a.m., Connie Jackson, a city spokeswoman, said.

The younger boy died at around 4:25 p.m. at University Hospital in Newark, Stacie Newton, a hospital spokeswoman, said.

No charges had been filed as of Saturday afternoon, but the case was being investigated by the police and the state child welfare agency, Ms. Jackson said.