According to the California Highway Patrol, the unidentified 11-year-old boy and 46-year-old woman were hit by a silver Suzuki while crossing the street in Watts around 9 p.m.
Authorities say the woman sustained a major head injury and the boy suffered minor injuries.
The two victims, who were trick-or-treating when they were hit, were taken to a local hospital for treatment.
Police found the car abandoned nearby south of 88th Street. According to a report by CHP, the car is registered out of Kent, Washington.
Authorities are searching for the suspects involved in the hit-and-run. A witness told police the three males in the vehicle jumped out of the car and fled the scene on foot.
The suspects were described as black males.