A 100-year-old man drove on to a pavement and hit 11 people, including nine children, opposite a primary school in South Los Angeles.
Los Angeles fire captain Jaime Moore said four of the children were critical when firefighters arrived but they were stabilised and now in a serious condition in hospital.
Capt Moore said some of the victims were trapped under the blue Cadillac before witnesses helped pull them out.
Police identified the driver as Preston Carter. Investigators talking to him said he was being co-operative.