It’s pretty obvious that a lot of people posting here haven’t read the Potter books. I read them all back in the days when they came out and there are two points here:
1) What is described as “magic” in the books has nothing to do with kishuf. It’s a genetically inherited ability to alter the physical world in ways “muggles” can’t. Thus it is similar to other genetic abilities like perfect pitch or perfect memory. There is no “paganism” involved. Far from seeking it, some wizards / witches actually seek to escape having it. The use of the terms “witches” and “wizards” is simply a play on the English words and doesn’t really refer to what most people over history have meant by them. Also, the wizarding world celebrates Xmas and Easter as well as Halloween (All Hallows Eve – instituted by the Roman Catholic church to replace a pagan holiday).
2) Having gone to public school, and spent years dodging my concerned friends who were trying to “save my soul,” I know far more about Xtianity than I would like. There is nothing in the books that is explicitly of that religion until the end of the very last book, in which Harry dies and is returned to life to save his friends. And if you didn’t know that was based on their doctrine, you might miss the religious reference altogether. Yes, the virtues of friendship, etc. are there, but there isn’t a visible element of religious belief that could be thought of as missionizing.
As far as religion goes, as far as I can see the books are OK. They’re well-written and keep kids’ attention while they build reading skills. Whether you allow your children to read them is up to you and your LOR. Books 4-7 of course have the characters as teenagers, and there are plot elements that don’t occur (we hope) in the frum world. If you allow your children to read secular fiction, I would recommend first reading the books yourself before giving them to your kids, and then deciding whether or not to allow them.