Cathe, I hope you can answer this better than I. But I know that you are doing a lot of work right now. So I will take a stab at addressing it until you see this thread.
Georgia and Sailingwidow (cute name!),
I have a book called "Strength Training for Young Athletes." I got it from the Human Kinetics site. I think you can access it by typing "Exrx" into your address bar.
Anyway, in the book are many caveats to know, in order to make strength training safe, enjoyable, and effective for youngsters. One thing I remember from the book, and that is that muscle hypertrophy, or size gains, will not occur until after puberty. It is influenced by the presence of hormones.
The authors of this book say that strength training is useful and effective, but that body-weight only, and calisthenic type exercises (think Boot Camp) are better suited to young physiques than heavier weights. It is a nice book to read, and if you could find it in the public library it would be useful to read.
A lot of the book is given over to designing strength training programs for schools, and is not very pertinint to my needs. So I wish I had found it in a library. I am keeping it for reference though, and if you have a specific question I'd be glad to look for it in the index.
Cathe has more knowledge about training in general, and her reply would probably answer your question more specifically. My take on it (I have an eleven-year-old boy) is that a certain maturity and patience level needs to be attained in order for a Cathe-type workout (as is) to be of benefit. However, you could probably shorten it (to match his attention span) and be his instructor for each workout session.
Full-body workouts with lower body work as the warm-up would be a good beginning.
HTH
-Connie
