I suggest using Chapman’s as your primary source; it covers all the basic small boat skills, and everything need for up to a 100 ton license. When I was about 12 an uncle took me to USCG Power Squadron night classes that were very good. You might want to contact the Power Squadron for materials. However, the best place to start is with the dozen most useful knots. At a very early age, I was taught to rapidly tie a bowline underwater in the dark. Kids can practice that by tying it behind their back. Line throwing contests are also good. For kids that are more academically inclined Rules of the Road and making flash cards by coloring in the proper lights area good exercises to learn this fundamental topic.
I wish someone would make a computer program like Flight Simulator to cover Rules of the Road and Shiphandling. Actually, Flight Simulator is good for learning how to make turns and to steady up on a course.