The crash happened at about 7 a.m. at Mona Boulevard and East 119th Street. The mother died at an area hospital, and her two children died at the scene.
CHP officials said a white Cadillac was headed southbound on Mona Boulevard at a high rate of speed., and a beige SUV was coming out of 119th Street, trying to make a left turn onto Mona Boulevard headed north. That's when the two cars collided, and the crash occurred with so much force that it sent the cars hurtling away from the intersection and onto a sidewalk.
The driver of the Cadillac was arrested on suspicion of driving under the influence.
The Coroner's Office identified the mother and two daughters as Lynzne Jane Martinez, 30, of Los Angeles; Loryana Martinez, 3; and Brianna Martinez, 7.
Mitzi Rendon, 16, said she heard the crash out of her bedroom window and ran out to help. She said she pulled one of the children out of the SUV's window. Wade Pitts also rushed to help. He helped pull an infant out of the SUV.
Survivors of the crash were transported to local hospitals with moderate injuries.
A candlelight vigil was held for the victims in the evening.
The cause of the collision remained under investigation Monday afternoon.