Harry Potter is growing up, and hopefully his audience with him. The British Board of Film Classification has rated Harry Potter and the Goblet of Fire 12A, which means no one under 12 can get in without a parent; while the American Classification and Rating Administration has rated it PG-13, which doesn’t really mean anything, except it sounds a little more serious than PG. All the previous Harry Potter films were rated PG in both countries.
FWIW, note also that Goblet of Fire — which is based on the second longest novel in the entire series — is said to be about 157 minutes long, which is about the average length of these films. To put this in some context, the shortest Harry Potter film to date is Prisoner of Azkaban, at 141 minutes; while the longest is Chamber of Secrets, at 161 minutes. (Philosopher’s Stone is 152 minutes.)