Again, I ask, where have I ever said this?
Notice how I said, “I suppose.” It means that I was not committed to that statement. I certainly believe that if the parent is an actual guardian, then the parent or whoever is responsible at the time in question (e.g. babysitter) is liable for the actions of someone who needs guardianship. If the person does not require guardianship, then they are definitely liable legally for their actions.
But I would really appreciate it if you would stop putting words in my mouth. I made no such claim that if an adult could not argue on his behalf, that the NAP did not apply to him.
I think you would benefit from reading A Praxeological Account of Law by Clayton.