I posted on this a couple of months ago, but still haven’t found out why the Cub Scouts and Boy Scouts, along with almost everyone else, wears “left” flags on the right shoulder of their uniforms.
UPDATE: Two seconds after posting this I googled and found the answer about the Boy Scout uniforms.
The [BSA National Uniform and Insignia] Committee determined that since the U.S. Code does NOT specifically address the direction the flag should be worn on an article of clothing, that the flag would be worn as if you are looking at that flag from afar, with the stars to the rear.
There you have it. I don’t agree with the decision, but the page also mentions that the Boy Scouts of America have no intention to change their minds.