Best Martial arts Style for train your Kids on self defense and Martial arts techniques:
Your child should start out with something that has to do with fast movements hitting kicking and jumping. Once he's a teen teach him balance concentration and patience.
For very young children, there should be some indication of achievement that they can earn at least every 1-2 weeks. This way they know when they have accomplished something, and they internalize that things like focus and practice are good strategies.

Martial arts are too dangerous for children so you have to choose Martial arts style that met your children capabilities and his/her body requirements, because of some Martial arts teaches confidence while another learn How to Kill other Guy not just a self-defence training, that what is the real danger for your kid to get learn it.

Is Karate the best MA for your Kid?
Training of Karate will give your Kid Discipline, self defense, staying focused, lots of conditioning, agility, respect. This is great for kids, it teaches them how to be adults, and respect others, doing karate since your Kid in 5, until 17 years old will teach Kids how to focus, which he can apply everywhere. At school He can just flick it on like a switch, very useful. Also perseverance and of course training physically and mentally . Indirect benefits - never get into fights because of rep, confidence, respect, and good morals. Pride and honor . Basically a good foundation for life . I've never regretted it. Some thing should know about Karate is that Traditional Karate may be suitable for children because it have traditional Fighting techniques that will not make danger to your teen kids.
I think karate is good for children because they will learn how to defend themselves. They learn how to jump, kick, stuff like that. I think it is better to let your kids train karate, no danger in Karate training; just simple focus and Morals, in addition to the Karate Class cost 40-100$ a month for karate lessons for any age, "Black Belt Factory" will be a little more expensive, but you'll have a black belt in 18-30 months.

Is Kung fu good to teach your children?
Chinese Martial arts is the other name of Kung fu, Kung fu fighting Styles are too dangerous for children because your Kids have to learn something like Tiger Claw or Drunken boxing, or even Warrior style, any way kung fu Martial arts style for children have an experienced Instructor who know the right steps to engage children in Kung fu trainings, so kung fu kid of age between 3 – 13 should only learn and Practice on Focus and breathing strategies beside fitness practices, then when they will be adult they could learn Warrior styles and animal styles

Is Brazilian jiu-jitsumake your childrn stronger?
BJJ for Kids can be safe and it can be dangerous. BJJ for Kids can be overly technical and not too technical. BJJ for Kids can be too rigorous and it can be administered correctly. Kids can understand BJJ, and they can find it too difficult.
It is another dangerous Martial arts for children because:
Belt Progress: Many children's programs to signal progress between the white and yellow belt rankings. The amount of time it takes to achieve the rank of black belt varies between the individual but the average time frame is between 8 and 10 years.
BJJ techniques: BJJ permits a wide variety of techniques to take the fight to the ground after taking a grip. While other combat sports, such as Judo and Wrestling almost always use a takedown to bring an opponent to the ground, in BJJ one option is to "pull guard." This entails obtaining some grip on the opponent and then bringing the fight or match onto the mat by sitting straight down or by jumping and wrapping the legs around the opponent.
BJJ instructor: If a BJJ instructor is overly zealous about pushing kids, it can be too rigorous. So BJJ should learned by best experienced Instructor.
An instructor who understands children and their growth patterns in relation to their physical, mental and emotional development will build a curriculum and class schedule that is 'just right.'

Is Taekwondo training suited for children ability?
I think it is not dangerous to children because it’s techniques aims on soft techniques and depend on the fitness and increase breathing ability for children also includes aerobic kicking movements as mostly a combat movements using legs jumping, Taekwondo kids learn complicated movements. Which help their concentration and memory. And they learn to coordinate their bodies.
For young boys especially. The tough physical training allows them to let off steam.
They love kicking and punching under controlled conditions.
But they also learn about self-control, how taekwondo has to stay in the Dojang, they learn from great role models, taekwondo for girls will being fit and healthy gives girls a positive body image, learning to face confrontation and fear and powering through wooden boards develops self esteem and self confidence.
Instructing students in Taekwondo is a difficult task requiring a large amount of patience, but teaching young children requires even more discipline than older students.

Summary:
We have listed the strongest Martial arts BJJ, Kung fu, Karate, and Taekwondo; to show you details about every martial arts way of training Kids Programs, then it is your turn to select what Martial arts style suitable for your children age and body capabilities.