One day when I was 9, I ran into a friend on my block while walking to school. He said he had something to show me, and we stepped into an apartment building vestibule. "This is my dad's" he said, producing a 6" blade automatic stiletto. "Want to try it?" When I pressed the release button, the knife's powerful spring sent it flying through the air. I remember thinking I would need to build some muscles before I played with another switchblade.
One day when I was 13, I ran into a friend from Boy Scouts while walking to school. I was going to the public school where I was in 8th grade, and my friend was going to the Catholic parochial school two blocks away. "Check this out" he said, producing a 9 MM Luger from his gym bag. It was his father's war souvenir. He said his father also had an MP 40 submachine gun which he had recently turned in to the police, and that he (my Boy Scout friend) would never ever forgive him for that! I remember thinking yes, a thing like that
would be hard to forgive.
When I was a child, I thought there was a war between children and adults, and that the children would eventually win but at a terrible cost. When my parents said "Piso, this is Mrs. Johnson who teaches at Hayt School," what I heard was "Mrs. Johnson, She Wolf of the SS."
I consider all of this normal childhood behavior. Normal is debatable, I suppose, but it is certainly very common. That is why your job as a parent is to help your children survive childhood!
You should explain to your son that fine kitchen knives stay in the kitchen to preserve their edges, and that knives under pillows is a very bad idea: if someone burst into his room at night, he would cut his own hand and drop the knife on the floor.
My First Victorinox would make a fine present.
You could find a safe place for it near his bed and show him how to sharpen it.
Ask if he's afraid of the dark, children will usually admit this. That's what night lights are for.