Yeah, kids were much smarter when their literature was about hard-nosed, serious subjects like a lion who rules over a magical kingdom in a closet. Or a young girl, a small dog, a talking lion, a tin man and a scarecrow dodging witches to find a wizard. Or princesses, pirates, knights of the round table, giants, orcs, hobbits, and teenaged detectives.
I agree the books are ok for young children. For HS and beyond they are more akin to comic books.