According to the Gardena Police Department, a driver crashed into the two pedestrians in the crosswalk at Marine and Budlong avenues around 10:30 a.m.
The driver fled the scene.
The boy's age wasn't immediately released, but Eyewitness News learned from family members he is under the age of 6.
Responding officers found the boy and his grandmother in the roadway. The grandmother was rushed to a nearby hospital but the young boy did not survive.
Residents in the area say drivers are constantly speeding through red lights at the intersection, saying they would like to see the city increase patrols.
"We just need more police over here, need more speed traps, we need more tickets given out, and maybe if there's heavy amount of that, they might slow down," said one resident. "Give it a shot, but they've got to do something about it."
A memorial has since been set up at the crash site filled with flowers and candles.
Anyone with information is urged to contact authorities.