Local authorities have set up a crisis centre to provide on-site medical assistance and counseling for victims and their relatives, the prefecture said.
Michele Alliot-Marie, the interior minister, and Dominique Bussereau, the transport minister, immediately travelled to the scene.
They called for full details to be disclosed on the circumstances of the crash, after meeting the head of the children's school.
According to initial data from the SNCF, the French rail company, the level crossing was functioning properly at the time, the spokeswoman said.
"Records from the control screens at the level crossing, which was remotely monitored, show that everything appears to have worked normally up until the accident," she said.
Later, a woman in a car behind the bus told France Info radio she saw the bus start to cross the track when the red warning lights were already flashing.
"The train came and it cut the bus in two," said the woman, whose name was not given on the radio report.