A driver jumped a curb and hit the three victims as they were walking in the area of Antonio Parkway and Oaktree Lane, south of Mission Viejo, around 4:15 p.m., according to the California Highway Patrol.
The three victims were transported to a hospital, but the child did not survive. The two adults were being treated for serious injuries, said Thanh Nguyen of the Orange County Fire Authority.
UPDATE: Suspect, victims identified in Mission Viejo crash
The child's age and their relationship to the other victims is unclear.
CHP said the driver was arrested on suspicion of DUI.
Footage from the scene showed the car with a damaged windshield that was stopped on an embankment next to the sidewalk.