HERE, is an article that address exactly that. I can tell you that, based on my experience, I totally agree with the author, especially the part about not all the time will be spent with line in the water. I can remember as a young kid taking time out from fishing to play around the stream. As a youngster, I knew quite well that I was NOT to disturb other anglers & to take care of my gear.
If you're thinking about taking a kid fishing, I applaud you. I think it's fantastic to see young anglers on the stream. Plus, you're working to create other life-long anglers who will keep the sport going, long after we're gone. Just be prepared. Understand that kids won't be into all the gear, the intricacies of wet & dry flies, or the technical aspects of the sport. That's fine. With teaching a kid to fish, it should be all about having fun.
So if you're trying to pass on fly fishing to the younger generation, I thank you. You're doing something great for the youngsters, the sport, & for yourself.