The bus was returning the children home from school Thursday in a mountainous village near the capital city of Hunan province when it fell into a pond, the Xinhua News Agency said.
The minivan was pulled out of the pond early Friday with the children and a driver inside, while the bodies of two teachers were found an hour later, Xinhua said.
The minivan was carrying 11 passengers even though it had only seven seats, Xinhua reported, citing the father of one of the children who died as saying it was common for the van to be overloaded.
An investigation is under way, the agency said.
Overcrowding on buses is common in China, where two years ago, 19 children died when a makeshift school bus for a kindergarten collided head-on with a truck. The bus had been converted from a nine-seat freight van, but was carrying 64 people at the time of the accident.
The crash caused public uproar about school bus safety in rural China, where there is a shortage of education funds and children are often forced to travel far to get an education because of school closures.