In "Back to the Future Part II," Marty McFly travels to October 21, 2015, to save his children, yet to be born in "Back to the Future's" 1985. For more check out this link (copy and paste!)
http://www.cnn.com/2015/10/20/entertainment/back-to-the-future-day-feat/
http://www.cnn.com/2015/10/20/entertainment/back-to-the-future-day-feat/