One day some boys brought scissors to school and shaved their heads.
I doubt if scissors can shave heads. Shouldn't the above be recast as the following? Your comments? Thanks.
One day some boys brought scissors to school and cut their hair.
One day some boys brought shaving knives to school and shaved their heads.
You are so right!
However in your second sentence, use "razors" instead of "shaving knives".
Not that I have met if you are talking about shaving the hair of the face.
The shaving knives I have met are used in woodwork.
I know if you do an internet search you find the term, but when you look at the images they are often of razors.