Many of our favorite TV shows find a way to stay on the air a long time, but they have to avoid many of the pitfalls that have killed the best of them. One sure sign that a veteran favorite may be dangerously close to "Jumping the Shark" is when they add a child actor to the cast to play a new brother, sister or cousin. Here are a few shows that lost their way once a child actor came on board: Cousin Oliver, “The Brady Bunch”; Olivia and Cousin Pam, “The Cosby Show"; Chrissy Seaver and Luke Brower, “Growing Pains”; Courtesy Everett Collection Avery Brown, “Murphy Brown”; Nicky Banks, “The Fresh Prince of Bel-Air”.