First thing I would check is what arm slot he is throwing from. Chances are it is the "natural" 3/4 arm slot. Chances also are that the ball has more of a "gyroball" spin on it (like a thrown football sprials). This also is perfectly natural, especially at a younger age.
Side spin occurs naturally from the 3/4 arm slot as the angle of release is brought more parallel with the ground. If your son's side/ gyro spin is caused by a low 3/4 arm release, do not change anything!!! I repeat, do not change anything!!!
My son started pitching when he was 9 years old in little league. He had been throwing baseballs ever since he could walk. He had a very low 3/4 arm slot when he bagan pitching (about 9:00 o'clock location) and continued with that same slot for three years. Over those three years I heard from everyone and their dog about how his throwing would hurt his arm (the low slot and not coming "over the top"). Well, 4 years later he has now polished off into the best pitcher in his age group. Not only does he throw harder than the other kids, he has crazy wicked movement on all of his pitches because of the lower arm slot. I contribute this all to just letting him throw how he feels is "natural". He is now thirteen and has moved his arm slot to just above 10:00 o'clock.
The rule I have always stood by is this- If he throws as hard or harder than anyone else, is consistant, and doesnt have joint pain then don't mess with the arm!. The body, in order to accelerate a 5 oz ball will "naturally" find the most effecient way to do this as long as you are not trying to work against yourself. Working against yourself means that you are worried about the height of your elbow or your release point or "coming over the top" (a very bad little league coaching philosophy!) and as such, you will find your body working against itself as you try to do things the body doesn't do effeciently.