Only one show has succeeded in keeping a kid in the lead for a decade: "The Simpsons" with the animated Bart Simpson. Watching Bart never mature is considered a key to its enduring appeal. "Early on, I know that the powers that be decided that no one would age," said Tim Long, the show's current head writer. "A kid with a starter ‘stache, that would just be unpleasant," he added.
Source: wiktionary