SBD is a really healthy way of eating. Your son can actually eat with you on this plan, though you want to have him in Phase III. Forming healthy eating habits for yourself now will really help your son as he gets older to form healthy habits of his own.
You can find more info in the FAQ stickies, and of course, you've read the book. Be aware that some people find that they don't have enough energy to exercise at their normal level during Phase 1, at least the first week. If you do, feel free, just pay attention to what your body is telling you and take it easy. In Phase 2, you can go back to the exercise you were doing...that definitely helps!