I'll admit something here:
I drove a 45hp tractor with a 10 ton trailer on crowded tourists roads to the fields at age 9. However when i first fired a gun, in Canada at my 15 years older Canadian cousin, a Remington hunting rifle, i felt uncomfortable and was scared about what i could do with that gun, and quickly handed it over back to him after firing two or three shots... You could say i felt unfit for the responsibility if it could do this much damage. However the 4.5mm pellet gun my father owns, (legally in Holland) i feel indifferent about it even when shooting at sticks in my friends hands, when aimed far enough off their hands... A 4.5mm pellet at close range, in worst case, can do just as many damage to someones hand than a solid bullet of a Remington, but its all about what you are brought up with.
While every idiot in the US can buy a gun, i am a bit astonished about your cautiousness about a pocket knife... Whenever visiting the US, being a European, it wouldnt be YOUR son, having a pocket knife, i would be worried about
And when your worry is about your son harming himself: I remember what a friend of mine admitted about when he was 10 years old and his older brother was bullying him to the end: He got so enraged that he went sharpening a knife on the grinding stone. When his grandpa asked what he was doing and he answered that his brother should die, grandpa said: Before you take the knife to your brother, make sure it is REALLY sharp: just feel with your finger, make no mistakes ! Then granda left him alone, sharpening the knife. When he tried the sharpness of the knife he instantly cut himself in the finger, and the pain made him forget his anger and kicked him right back into reality... Just as grandpa knew would happen