The original script for 1978’s Halloween was titled “The Babysitter Murders.” In it, the events took place over several days. The script was changed to have everything happen on the same day as a budgetary decision. It reduced the number of costume changes and locations required. It was decided that Halloween, the scariest night of the year, was the perfect night for this to happen.
Of the female leads (who were all supposed to be in high school), only Jamie Lee Curtis was actually a teenager at the time of shooting.
Discover more behind-the-scenes facts at IMDb: Halloween (1978) Trivia.