One member of the family, a 13-year-old boy, survived because he stayed behind when the other members of the family took their trip.
The dead were identified as the parents, Arturo Lopez and Irene Sosa, 35; Cynthia Lopez-Sosa, 12; Danira Lopez-Sosa, 7; and 11-month-old William, who was to have a birthday, said N.C. Highway Patrol Trooper D.J. Reid.
The family had driven to a party supply shop in Hickory and was on its way home in a 1996 Ford Explorer, which ran down a 12-foot embankment on U.S. 70 about two miles from Statesville.
The youngest was secured in a child safety seat, but the seat wasn't attached to the vehicle, the trooper said. The other children were not wearing seat belts.
Trooper D.J. Reid told the Charlotte Observer the SUV likely was traveling at the posted 55 mph speed limit, but that that was too fast for the conditions.
The parents and two oldest children were from Mexico. The two youngest children had been born in the U.S.