Harry Potter movies made many actors very famous. Emma Watson, Rupert Grint and Daniel Redcliffe became an A-list celebrities. Despite the popularity Harry Potter cast has to follow stick Warner Bros rules.
Good Grades in School
The young cast of Harry Potter spent a large portion of their childhood on film sets, but that doesn't mean that they were given a pass on school work. All the young actors had to keep up their grades to keep their jobs - and yes - they went to classes in their wizarding robes!
The rumor is that Tom Felton was once kicked off the set for "chocolate". Apparently, the actor used to carry snacks in his robe, including chocolate candies. In hot weather, the snacks would melt, which would add to the dressers' workload.
Wait, aren't we talking about children's movies? What does alcohol have to do with this? Well, by the time the last part of the franchise was filmed, the actors were already adults. Given the fact that they were incredibly popular and received high salaries, the problem becomes apparent.
No American Actors
This rule actually implied not hiring non-British actors, and it was introduced by Joanne Rowling herself. The writer really wanted the British characters to be portrayed by British actors. However, in Fantastic Beasts, there was no such rule, as the main events of the movies took place in the USA, so the actors could also be American.
They Had To Keep Secret the Plot
When it comes to dealing with a movie franchise as big as Harry Potter, it's vital that the actors don't accidentally leak any spoilers. While filming the movie series, J.K Rowling would often confide in the young actors about what she was writing next; information they had to keep on the down-low.