I am not sure if I am going to get the name of the show correctly, because I stopped watching it at some point when I was in High School which, was a long time ago. I am thinking of Suit Life of Zack and Cody?
Edit: Since you got me thinking, two more non-animated crossed my mind. The first although is a series, inside the series they do end up growing older, but in the end they end up becoming kids again at the end of each series movie. The first one is the movie series for "The Lion, The Witch, and The Wardrobe". The second one although the actor was not neccessarily a kid, they were 34 years old when the series started, but the length of the still ongoing series does start to show their age if you compare the lastest and first film in the series. I am referring to Tom Cruz in the film series Mission Impossible.