When I was about 6 years old, I became very interested in baseball. My father, being English, had no clue about the sport, so he bought me the MLB umpire's rule book. I read and re-read that book cover-to-cover and have loved the game ever since.
Fast forward to 11th grade. The basketball coach was riding my azz to play because I was 6'8" 220lbs and fast. I kept asking him what the rules were, but he would never tell me. All I did, day after day, was take shots and run laps. I quit basketball as soon as I could. It seemed like a pointless endeavor. I NEEDED direction, a plan-of-action, a goal.
Finally, a few years ago, a girlfriend of mine who was an avid Duke fan taught me the rules of basketball. I now find it almost enjoyable to watch.
An intelligent child needs to learn the rules and structure of any game to enjoy it thoroughly past the basic fun of kicking a ball about.
I would recommend buying an assortment of books on soccer, at various levels of reading comprehension, and leave them where your child can find them. Somewhere he will find what he needs and will either build upon his enthusiasm or decide that soccer isn't his path. Or he may just skip 3 grades in reading.
Either way... When you pick your kid up early at practice and you see the coach screaming at him as he runs laps or does pushups (and the coach is smoking a Marlboro and drinking Apple Schnapps from the bottle)... You will understand what I am saying.
At that age the coach could teach them positions and what not but it wouldn't matter by game time, it always ends up a free for all. Your son will learn more as he goes up in division.