That's not the question that was put to you. The question was, if civil law was consonent with the bible on the question of suffering witches to live, would it be moral for us to kill my 14 year old wikkan neighbor? Lynch mobbery is not being suggested, and not at issue. Good dodging of the question, though.
First recognize that you have shifted the question from an adult to a child. Even Israel had Judges to deal with tough questions. I think it's entirely appropriate to be prosecute a 14 year old child in juvenile court, if he practices witchcraft in a jurisdiction where it is illegal. I think how you ajudicate children is different than how you ajudicate adults and always has been even in early Israel. Depending on the situation there are many alternatives available to the judge.