I think textual descriptions of child sex are, strangely, still legal, if only because a lot of literature has included them.
The book is written from the perspective of a pedofile lusting after a young girl. Stanley Kubrik's film of the movie in 1962 won an academy award. There was an immense ammount of controversy surround the movie and the book, and they still are. Art or obscenity? We'll be having this discussion for years to come.
Neither movie contains anything explicit beyond kissing, as I recall. But there's no doubt what's going on.