Listen, kids. What we have to acknowledge here is that Harry Potter doesn’t live in our world, where “magic” and the occult are synonyms, where the kinds of things that take place in the books can only come either from direct collaboration with Satan (whether knowingly or not) or from the direct intervention of God.
Rather, the world in which Harry Potter lives, the one invented by J.K. Rowling, and not the one created by God (the real world), is one in which magical ability is not a result of the intervention of spiritual beings, but is in fact an ability which corresponds, as far as I can tell, with musical, mathematical, or linguistic ability. Essentially, in the world of Harry Potter, magic simply is not the evil that it is in our world.
Now, the argument that Harry Potter can possibly corrupt children remains, if you are willing to adapt it to saying that children are incapable of seeing that Harry Potter is fiction and that reality is fact. However, anyone who can distinguish fact from fiction should be able to distinguish the occult from the fictional magic of Harry Potter (which, incidentally, is the same fictional magic that allows wizards to be wizards throughout LOTR, Arthurian legends, and the like).
Thus, the morality of the books boils down more to a subjective determination of whether a child will be deceived into thinking that the things done in the book can be sinlessly done in the real world. And that, dear friends, is a determination that lies mostly with age.
There endeth the lesson.