This would be the end of that teachers carrier. Not relocating the class to a heated room, or if can't sending them home. Its if the weather is freezing she is endangering every child in the class. She even let a window get opened dropping the rooms temp. Then also allowing the children to strip and drop their core temps, on top of the problem of children stripping this further endangers them to the cold.
The shear level of negligence is insane, to the point she would probably be looking at criminal charges.