I am not too familiar with traditional martial arts such as karate, tae kwon do, and kung fu. These have been around for a long time.
From what I have seen in class from chopping up boards and punching air, I’m sure there is a lot more, but what I do know is that the combat is all stand up.
How many real fights have you seen? How many of them stay standing up? I would say none. They all seem to throw some punches and then wrestle each other to the ground.
Jiu-Jitsu is all ground fighting (where the fight goes 99% of the time). Submissions and positioning wins those type of fights or any fight, Takedowns are extremely easy to get against a anyone who is only a stand up fighter whether it be a boxer or a karate master.
Floyd Mayweather, the best boxer in the world, would not win a fight against a college wrestler because he has no idea how to defend a double leg takedown.
If you’re trying to get your child into some sort of martial arts, I recommend Judo, Jiu-Jitsu, or even Muy Thai.
Those are going to be the most common uses in an actual fight.
Photo above: Erick Silva locking in an armbar against Jason High at UFC on Fuel 10
Thomas W 
Cool