The National Transportation Safety Board is sending investigators to the scene of a crash between two Tennessee school buses that killed two small children and a teacher's aide.

Knoxville police identified the victims of the Tuesday afternoon crash as Zykia Burns and Seraya Glasper, both 7 years old, and 46-year-old Kimberly Riddle.

A preliminary investigation found that the buses were traveling in opposite directions on the Asheville Highway when one of the drivers made a sudden left turn across the concrete median and crashed into the other bus.

The second bus flipped onto its side. Three people in that bus died, and another three suffered serious injuries.

The children had been traveling home from school. Police have not said why they believe the driver of the first bus crossed the median.