The basic point of the video below has been made by many people already, but it’s still fun to see that point illustrated with clips from the movies themselves. I think the main thing missing is the fact that, if I recall correctly, both Forrest Gump and Benjamin Button are concerned that their offspring be more “normal” than them.
http://player.ordienetworks.com/flash/fodplayer.swf
Click here if the video file above doesn’t play properly.