I would love to see any of the kids from the first three Digimon seasons. I was a huge fan of the show as a kid. Mimi, Izzy and Davis were my favourites. Rika was my favourite tamer, and man, her fashion sense has stood the test of time. I would wear that outfit today.
Here are some suggestions that I'd think be good: The Rowdyruff Boys Invader Zim Legend of Korra Adventure Time Charlie Brown The Boondocks The Simpsons Kids Yu Gi Oh (The original series) (Maybe even some Disney Princesses)
I'll just create a list of different shows and/or characters, I know most of these don't match the theme of these works, but I am going to leave them here because I can...
Invader Zim Digimon Archies Arthur I do want to see KND, Teen Titans, Jimmy Neutron, Danny Phantom. I also want to see The Mystery Incorporated Gang as adult paranormal investagators/myth debunkers/crime investagating vigilanties they truely are!
A list of child aged characters I'd like to see from shows that don't have a main cast of children: Mac, Goo, Terrence, and Frankie from Foster's Home for Imaginary Friends Penny from Inspector Gadget Kevin with Krypto the Super Dog, Cyberspace (yes that educational show) Dora the Explorer (Yes that educational show) Gravity Falls
Some of the children from Classic Disney Movies. (Peter Pan, Alice in Wonderland, Wart from Sword and the Stone, etc.)
All the Disney Princesses in the canon line up are canonically teenagers with Snow White being the youngest at 14 and Cinderella and Tianna oldest at 19.