The shooting happened just after 9 p.m. in the 1900 block of Corning Avenue, near the 10 Freeway.
Police said two adults were also injured. An adult female victim suffered minor wounds, and an adult male was hit in the torso but is expected to survive.
The little boy, who is said to be about 9 years old, was in critical condition, according to officials.
No suspect description was immediately available. Police said they were looking for a white car.
DEVELOPING: We'll add more details as they become available.