Trivia: Cary Fukunaga, whom is perhaps best known as a director on the series "True Detective" and for his works on films like "Jane Eyre", was originally contracted to write and direct the film. He eventually left the project after creative clashes with the studio, as he wanted to make a more unconventional film and executives feared his vision would not sit well with mainstream audiences. Fukunaga is still credited in the final film as a co-writer, however as many scenes from his version of the script were preserved in the final film.
Trivia: Bill Skarsgård was purposely kept separated from the child-actors during filming, and outside of some early publicity photos, the kids never saw him until the first scene they filmed together in order to get their genuine reactions. The kids were both genuinely scared of him, but also incredibly excited after filming their first scene.