Most 12 year olds are at an age where they can handle watching a movie like Knives Out. The film is rated PG-13, which means that it may be suitable for children under 13 only with parental guidance. There are a few scenes in the movie that could be frightening or disturbing for younger children, but overall the film is lighthearted and humorous. If your child is a fan of mystery movies or books, then they will likely enjoy Knives Out.