http://www.imdb.com/title/tt0100666/

A crew of Martians overhears a radio broadcast of Orson Welle's _War of the Worlds_ coming from Earth, and, thinking the Martian fleet is attacking Earth, they land their broken-down ship in a backwater mid-American town. As luck would have it, they land on Halloween and get mistaken for trick-or-treaters. Comedy ensues as the Martians try to get taken seriously. 

When one saucer of an invasion force has engine trouble, it lands on Earth. It happens to be Halloween and it happens the invaders are only about 4 feet tall. As the bumbling aliens wander around the countryside they are taken to be children and they make friends with two children, one of whom is the daughter of the sheriff. As their troubles mount (it's difficult for five aliens to conquer a world) they begin to give up their plans of conquest, but then there is that nasty killer robot.