You could argue with a theist until you're blue in the face but if their faith is deeply held you'll get nowhere.
A change in their belief must come subsequent to a self-realization that what they previously believed was the truth is, in fact, a lie. Children are not born religious; it's what they are told by their parents in their formative years and then by organized religion that makes them "believe" in a supernatural entity that is responsible for the existence of everything around us.
The conversion to Atheism and the real truth must come from examination of what they've been told and the realization of how ludicrous it is.
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