There are many different styles out there. If I may suggest, get a list of the schools in your area.  Then I would take a visit to each one. Most schools will allow you to watch for a bit. You can get a very good idea of the qualitly of the school, teachers and other students.

Once you visit a few you will get an idea of which is the best style for you son.

If you dont like a particular style you can always change schools. Many student study several types of martial arts until they find their favorite.

What part of the country are you from?

Gook luck in your search.

Also make sure that the school you go to specializes in kids training.
There are many schools that only teach adults.

I have found this wonderful article hope it is useful for you.

Ten Things You Should Know about Martial Arts Summer Camps for Kids

Author: Paul M.  Jerard Jr.

Would you like to see your child gain self-confidence, learn goal setting skills, concentrate, gain self-discipline, and acquire life skills that he or she will have for a lifetime? Of course you do; we all want the best for our children.
 A Martial Arts Summer Camp is a complete success enhancement program for your child, which will challenge his or her mind and body. Here are just ten of the many benefits you can expect your child to receive in just one summer.
 Concentration: Your child will learn to increase his or her attention span. Focusing is major problem for children; especially for boys, but martial arts are completely filled with concentration drills.
 Stress Management: Kids are taught how to constructively deal with stress. Just by getting some physical activity, behavior will improve when children come home. Without recess and physical education, children have a lot of "bottled up" energy.
 Self-Discipline: Your child is taught how to set priorities and get ahead. Children have to multi-task, but martial arts training will give them perseverance and the ability to prioritize their daily lives for success.
 Respect: Your child will demonstrate courtesy and respect at home. How? Once he or she practices courtesy and respect all day - this habit will be carried home.
 Anger Management: We provide a safe outlet for dealing with anger. Kicking and punching bags is very safe, if supervised by a qualified martial arts instructor. This allows kids to "blow off some steam," without hurting themselves.
 Motivation: Your child will be inspired to achieve. Positive energy is rampant, within a martial arts setting, and this inspires children to excel in every aspect of their lives. As you already know, motivation is what turns dreamers into achievers.
 Self-Defense: Every child will learn physical and non-physical self defense. As a by-product of attending a martial arts intensive, such as a kid's summer camp, every child can adequately protect him or herself.
 Total Fitness: Children receive a complete workout every day they attend a martial arts summer camp. It is not natural for children to sit in front of a television set all day. It is much healthier for them to run, kick, jump, and yell. This also helps them sleep better, too.
 Time Management: Your child will learn many time saving drills that make your life easier. Children need to have structure and order gently reinforced, so that it can be ingrained within their consciousness.
 Goal Setting: This is contagious in a Martial Arts atmosphere. When your child earns his or her first colored belt, he or she realizes goals by continually putting forth effort. This skill is also applied to an academic setting for maximum success.
 These are ten of the many life skills your child, will gain from a Martial Arts Summer Camp.
 ? Copyright 2006 - Paul Jerard / Aura Publications

Article Source: http://www.articlesbase.com/sports-articles/ten-things-you-should-know-about-martial-arts-summer-camps-for-kids-24210.html

About the Author:
Paul Jerard is director of Yoga teacher training at Aura in RI. He's a master instructor of martial arts and Yoga. He teaches that along with fitness. He wrote: Is Running a Yoga Business Right for You? For Yoga students who want to be a teacher.
 http://www.yoga-teacher-training.org/index.html