M.D.
Boy, could I tell some stories! Why, oh why, is it that they pick up on that immediately and not imitate "please" and "thank you" as well?
It worked pretty well for me to say "that is a grown up word". I also started using a funny version myself, e.g. when something is BS I say "horse feathers", or "wombat" when I mean "damn it".
Just keep downplaying it and it will go away, at least until around 5th grade - lol