This is incredibly sad. However, maybe more consideration is needed about the actual danger of the situation. The child was a 17 year old boy. Most 17 year old boys I know are taller and stronger than both parents. He had a knife and was being violent, so they called the police. If you believe that a knife is not an extremely deadly weapon, do a Youtube search for knife attacks. There are a LOT of recorded multiple stabbings (fatal ones) by a single person against police. And if you are unsure how a Tazer works, they do not have the same effect on all people. Some can just shake it off. It happens all the time.

But I could be completely wrong and the body cams will show that when they are released.