A school bus full of students crashed into a tree this morning in Butler County.
Police say 7 people were taken to the hospital including 3 children.
Upmc says 2 of the children were discharged from the hospital and the third is in good condition.
The bus was carrying elementary school students from the Mars Area School District.
A mass casualty incident was declared to get enough EMS resources to the scene.
The crash remains under investigation.