The collision occurred at the intersection of Ramona Drive and Central Avenue in Santa Ana.
Police say Carmen Teresa Silva, 51, was walking her grandchildren to school when a teen driver hit her and her 6-year-old grandson. Her 7-year-old granddaughter was not struck. The boy died Monday in a hospital.
Authorities say a 17-year old Segerstrom Fundamental High School student was driving his 13-year old brother to MacArthur Fundamental Intermediate School when the accident happened. The teen stayed at the scene and cooperated with investigators.