Quoting AmandaBlackfield:" I agree that any sport is dangerous... But nevertheless, I think that it's better to go in for sport ... [snip!] ... can't do any physical harm. So, I think I should agree for taekwondo as it's not so dangerous as karate. Thank you so much!"
Computer games absolutely can cause physical harm. Obesity, short attention span, low muscle tone, etc
And There is the same amount of risk in any martial arts. But the risk is so low. They rarely let kids spar, and even then, it is only for kids are a higher belt level.
Gotta let kids be kids and kids get hurt. Just a fact of life.