PG-13 rated stories are not suitable for pre-teens
PG-13 rated stories may contain content you would find unsuitable for pre-teens. This is typically due to more explicitly described violence, nudity, or use of profanity than you would find in a PG rating. However, those elements are not the main theme of the story.
It is your responsibility to read the story descriptions to ensure that individual stories do not contain themes you do not want your children to read.