The 1994 film Léon: The Professional, written and directed by French filmmaker Luc Besson, is about a paid assassin who takes in a 12-year-old orphan. The actress playing the orphan Mathilda was 11-year-old Natalie Portman in her first feature film. What happened after the film is interesting, too.
The movie wasn't a blockbuster, but was successful, grossing three times its production budget, and garnering good critical reviews. It is now considered a cult classic. Read more movie trivia about Léon: The Professional at TVOM.