The official Xinhua News Agency said the accident took place Friday in Longnan city in Gansu province and also killed one villager. Six people were injured.
The light truck was carrying 13 people, including eight schoolchildren, when it went off the road and tumbled 200 meters (656 feet) down a slope, Xinhua said.
The report did not mention the children's ages.
School buses are often in short supply in China, especially in rural areas, and overloading is a common concern on the country's roads.