UNITED Nations CHILDREN's AGENCY UNICEF appointed Millie Bobby Brown, the star of hit Netflix series "Stranger THINGS", as its youngest ever goodwill ambassador. And the 14-year-old had a message for world leaders: "Listen to us." The appointment - marked on World Children's Day at United Nations Headquarters and the Empire State Building in New York - MAKES the 14-year-old UNICEF's youngest-ever Goodwill Ambassador.