Surrey Police is appealing for witnesses following the fatal collision in Ewell, Surrey, today.
A Ford Focus and a Ford Fiesta were involved in the accident which happened in Banstead Road at about 10.30am.
A 29-year-old woman and her son have died and their next-of-kin have been informed by police.
A Surrey Police spokesman said: "Three people suffered serious injuries, one of whom is in a life-threatening condition. They have been taken to hospitals in London."
The road was closed following the accident to enable crash investigators to examine the scene and clear the vehicles and debris