The boy, Joshua Montes, was killed and his uncle was critically wounded when they were both struck in the head. Police said the man was holding his nephew in the backyard of his home on the 1200 Block of East 55th Street around 8:30 p.m. when the shots were fired.
The boy was pronounced dead at a nearby hospital. Police said the victims were not the intended targets, and it appears the gunfire came from somewhere on Hooper Street.
The boy's uncle was on life support in the hospital.
"It looks like they did go through some vehicle and then passed through a fence, and maybe have even gone through another fence. So it did travel quite a distance," said Los Angeles Police Capt. Mark Olvera.
Police are trying to determine if the shooter was on foot or if the incident was a drive-by shooting.
Police have no suspects. The incident remained under investigation Tuesday.
Anyone with information related to the case should contact the Los Angeles Police Dept. at (877) LAPD-24-7.