I wasn't commenting on your thoughts, just on what you said.

I found Ron's actions to be immature. He acted impulsively after he got his thumb sliced open. Was it wrong? Yes. Was it morally reprehensible? No, not any more than the action that caused him to retaliate.

This analogy just doesn't make it for me. There is a huge difference between endangering a child and what Ron did. In your example there is real danger of serious or fatal harm. But, there was no real danger to the twins. Not only was the knife not capable of inflicting a fatal wound, but the twins were quite capable of thwarting any damage at all. If Ron had charged the twin and plunged the knife into his heart or his eye, then you might have a point.