What movie from the 80's or 90's has two boys looking for a Unicorn they found once who's absence makes the smallest boy sick? I remember only a couple scenes like the youngest boy/brother leaning over a steaming mixing bowl with a towel over his head coughing since the unicorn left, and the Unicorn running on a beach at night. I remember the youngest boys proximity to the unicorn made his health dependent on its presence, and that they are trying to find it, but I can't seem to remember the name of the movie. Does anyone know what it is?