Any actor, both main or side.
I remember when Miranda was just a little tyke in School of Rock, then in Drake and Josh. She grew a lot during the latter show, but I don't think she's grown that much in iCarly; she looks the youngest out of the trio.
Jennette has.. She looks more adult then she did a few years ago. But.. What's his name, Nathan, has grown way more then all three of them. Gibby's actor and Nevel's actor have grown a lot too, especially Reed.