The search was on Friday night for a hit and run driver who police say killed two young children and critically injured their mother as they were crossing the street.
It happened in Denver just before 8 p.m.
Police say a 5-year-old was pronounced dead at the scene and a 7-year-old died after being taken to Children's Hospital Colorado.
Officers say they are looking for a large white SUV, possible a Cadillac with front end damage.
They say the woman and children were not in a crosswalk when they were hit.