Authorities say a black Honda SUV lost control for unknown reasons while in the northbound lanes of the freeway south of Imperial Highway just before 9 a.m. The vehicle went off the side of the roadway, flew over a fence and slammed into a tree.
Drivers of several other vehicles stopped to help the occupants in the overturned vehicle.
A 4-year-old girl and a 6-year-old girl were declared dead at the scene. Three other people were hospitalized: a 5-year-old boy is in critical condition, an 8-year-old boy has minor injuries and the driver, who is the mother of at least one of the children, is in critical condition.
Authorities say everyone was wearing seatbelts. The cause of the accident remains under investigation.