The gunman, who was not immediately identified, was fatally shot by police after a car chase, officials said, AFP reported.
The incident took place in the city of Shreveport, in north-western Louisiana.
“This is a rather extensive crime scene spanning between two residences,” police Corporal Chris Bordelon told a press conference, adding that a third residence was also part of the scene being combed by investigators.
The victims ranged in age from one to 14, Bordelon said.
“Some of the children inside were his descendants,” he added.
Two other people were struck by gunfire, but their conditions were not immediately known.
The incident, believed to have taken place around noon on April 19, is understood to have involved two men and a woman.
The suspect carjacked a vehicle and led police on a chase before officers opened fire and the assailant was killed.
“We do believe him to be the only individual that fired gunshots at these locations,” Bordelon said, calling the incident a “domestic disturbance.”
The United States, where firearms are readily available, is a frequent scene of gun violence, with thousands of people killed every year.
“It’s a terrible morning in Shreveport and we all mourn with the victims,” Mayor Tom Arceneaux said at the press conference.