This isn't the WTF part. Unexploded bombs and mines are a very real problem, resulting in deaths and deformities by the thousands.
Here's the WTF part....
The teachers called the kids back to class with a bell that was actually an unexploded bomb. The teachers rang it by hitting it with a stone. The head was confirmed active -- had the strikes been any harder, it would have detonated.
Hopefully, everyone knows better now.