If U.S. Marines invading Japan had been met by some of those same children, armed and killing U.S. Marines, I would find it difficult to claim moral superiority.
Had the Japanese experienced more success in the War and invaded California and, knowing some of the misconduct by Japanese forces in China and elsewhere, I am not sure that I would consider it a war crime to arm American children.
Too many Americans, I think, want to pretend that war is like a refereed boxing match, rather than the life or death struggle that it virtually always becomes.
Too many Americans want to pretend that war is a video game.