When it comes to batting stances, most hitters go by feel. Because, ultimately, it's about being comfortable and confident in the batter's box. Hitting at any level boils down to two things: see the ball and hit the ball. So you want your stance to help you do those two things.
From what I've seen and heard, I take a different approach than most in terms of teaching kids about hitting and batting stances. At the younger levels -- up to age 8 or 9 -- it's about having fun and making contact. I tend to keep it simple: I don't care about a 7-year-old's batting stance or how he holds his hands. Just see it, hit it and run the bases ... and have fun!
As players get older, you can give them more information and more teaching tips. The guys at my baseball camp this summer are 14-18 years old. They want to know: How do I get to that ball inside? Where should I hold my hands? How can I handle the breaking ball? What about the size of my bat?