The incident happened in the 2000 block of South Corning Street around 7:30 p.m. Wednesday.
Police say at least two of the victims were sitting in a parked car, when someone opened fire on them from a passing car.
The boy was treated at the scene for cuts from glass fragments. The two adults were taken to the hospital but are expected to recover.
Police don't know the motive for the shooting. They say the victims were not gang members, but it's unknown if the suspects are gang members. Investigators are looking for two or three suspects.
Authorities say there has been an increase in shootings in the area, but it's unknown if the drive-by shooting is related to recent activities.
If you have any information about this case, you're urged to contact police at (877) LAPD-24-7.