Lanyards not only are practical in that they help you to hold onto and keep from dropping things but they also provide emergency supplies. An inch of knotted lanyard can take up to 12 inches of cord to make. If you find yourself in an emergency situation needing cord you simply unravel your lanyard and have a supply of strong cord. And boys seem to love the idea of being in an emergency situation. And there are many different styles of knots to learn which means this is a craft that can be practiced for quite awhile.
My husband learned techniques for making lanyards from youtube videos. Simply entering the phrase, "paracord lanyard" in the youtube search yields many tutorials. My favorite of the videos my husband showed me is this one which is taught by a young boy. I can't recommend all his videos as I have only watched this one so as with all youtube videos...check it out before showing your child!
There are some really good books on knot tying that a child who wants to pursue this craft may want to look at. I recently found an exhaustive resource at a library book sale, "Encyclopedia of Knots and Fancy Rope Work." I just enjoy looking at this book! You can find some other resources here. There is also a fantastic site called Animated Knots by Greg that is so helpful. A pdf booklet on knot tying is also available at the Scoutmaster blog.