There are children’s movies, and then there are movies that are straight-up childish. Robert Zemeckis’ “The Witches,” the second adaptation of Roald Dahl’s novel of the same name arriving 30 years after Nicolas Roeg directed his own, falls squarely under the latter designation. Instead of a movie for children, Zemeckis’ film panders to children and goes so far overboard that it winds up pandering at them. Kids deserve good movies. They deserve good horror movies, too, especially as the world grows bleaker by the day and necessitates tools for giving the bleakness context. Horror can’t send the darkness away but can at least make it go down more easily; nothing’s scarier than not understanding why there’s darkness in the first place.