"Do you believe that all magic in childrens books is bad?"
Yes, I do. And I say this based upon what God says about the subject.
It's clearly stated in the Bible many times that all forms of witchcraft, magic, wizards, astrology, etc., are wrong in the eyes of God and, even as stated earlier, are actually an abomination in His eyes.
This is His Word, not just human opinion.
So, yes, anything that someone writes or produces which has occultic forms in it, whether it be "bad" witches or "good" witches, whether it be Mickey Mouse wizards or young boys and girls casting spells --- all of it is wrong according to the judgment God has already given in His Word.
He has already stated that it is wrong, and no one can change that fact.
If some people want to try to get around this by saying oh, this is only a story, it's not real.....I don't think God will be fooled. That's like saying it would be fine to have children's books about prostitutes, drug dealers, and gang murders because, well, it's only a story.
What people tend to forget is that God says these things for our good. He alone knows what's good for us and what's not good for us.
And He has very strong judgments against magic.
"This is His Word, not just human opinion."
(Referring to the Bible-- in my above post. Just wanted to clarify that.)