Every year the American Library Association's Office for Intellectual Freedom compiles a list of the top 10 most frequently "challenged" books. All these titles have been the subject of a formal, written complaint, filed with a library or school, requesting that they be removed. Sexual explicitness was the most common category of complaint levelled at books between 1990 and 2009. Indeed, Fifty Shades of Grey appears in the ALA list at number four. So it seems strange that a series aimed at seven-year-olds would top the complained about list for the second year in a row.

It must be noted that chapter 16 of the first book in the series is called the Extremely Graphic Violence Chapter. There's even a warning: "The following chapter contains graphic scenes showing two boys beating the tar out of a couple of robots."