This film has raised a little bit of controversy due to its high levels of violence and profanity, but it's also got a very positive message and is a film with heart.
I can't recommend this film for children, because the violence is bloody, over-the-top, and frighteningly realistic. There's also constant use of strong profanity (especially the f-word) including one use of c-word uttered by a child. The sexual content is at a PG-13 level, consisting of an implied sex scene and a few crude jokes.
However, despite the film's mature content, it's a very positive film with a great message. The film teaches that everyone has a responsibility to help their neighbor, and that you don't need superpowers to help someone in need. The film also conveys a strong sense of love and family through Hit-Girl and her father. This film has a lot of mature content, but it's really nothing worse than what you'll hear in the halls of an average high school. This isn't a film for kids, but I strongly recommend it to older teens due to its positive message.