If you are worried about your son loosing the knife, ensure that whatever knife you get him has a hole in it for either a small length of 550 or old shortened boot lace or small thin carabiner then he can attach to the belt or belt loop on his pants. Also really ingrain into your son that the knife goes back on the belt loop as soon as he is done with it...no matter what. Soon it will become a habit that will hopefully follow him throughout his life.