Who was this visitor? What was the book he spoke of?
Act out the events of the first section of the Testimony of the prophet Joseph Smith. You'll need someone be Joseph, someone to be the angel, someone to shine a light on the angel (this is a good job for really small children - or they may enjoy just watching), and 1 or more family members to narrate or read everything other than the angel's parts (starting with "He called me by name..." to the end of the section - "that God had prepared them for the purpose of translating the book."
Many people say that Joseph Smith made up the stories about being visited by Heavenly Father and Jesus Christ and then later by Angel Moroni. What can you do to find out for yourself if it's true? Have you done that? What happened? Challenge family members to pray to know whether this really happened.