So my son's first day at a new school comes home with bruises up and down his arms and broken skin on his under arm that looks like nails being dugged into his skin, but the school says he did it to himself and my son is four and can't really say much other than "he hurt me."

my son has never done this before and if there was a camera in the class room it would show the truth. I would say yes they should all have cameras because it protects everyone including the teacher because it will show what really happened regardless of what people say.