This review for the newest Harry Potter movie ends with this-
‘ “Harry Potter and the Goblet of Fire,” a Warner Bros. Pictures release, is rated PG-13 for sequences of fantasy violence and frightening images…’

Also, the article states there is a difference between reading the book and watching the movie,
“But reading it on the page and seeing it on the screen can be two entirely different experiences, and several scenes will be disturbing to viewers regardless of age.’

Violent images imprint on your mind, and it is difficult for young children to over come this trama.