I don't think there is such a thing as a bad book for children. Every now and again it becomes fashionable among some adults to point at a subset of children's books, a genre, perhaps, or an author, and to declare them bad books, books that children should be stopped from reading. I've seen it happen over and over; Enid Blyton was declared a bad author, so was R. L. Stine, so were dozens of others. Comics have been decried as fostering illiteracy. It's tosh. It's snobbery and it's foolishness. There are no bad authors for children, that children like and want to read and seek out, because every child is different.