At about 6 p.m., a male driver of a 1995 beige Nissan Maxima struck the woman and child in a crosswalk at Guinida Lane, then fled the scene.
An official with the California Highway Patrol said the driver was speeding.
Police said the car, which had been reported stolen from the nearby city of Stanton, was found abandoned several blocks away.
Nearby residents found the mother and child lying in the street, surrounded by clothing, stroller parts, a shoe and stuffed animal, among other debris.
"The little baby, she was laid flat down on the curb, no moving or nothing. The mother was on her back yelling and screaming, didn't know what happened," said witness David Acosta.
Both were taken to a hospital in critical condition. The girl died shortly after.
Residents said they have been asking for a stop light at the dimly lit intersection.
Anyone with information is asked to call the CHP at (949) 559-7888.
The Associated Press contributed to this report.