Avatar: The Last Airbender

In the 2nd and 3rd seasons of Avatar, Toph, who is the earthbending teacher for Aang, is barefoot all of the time.

In the 2nd or 3rd part of the "Sozen's Comet" series finale, Princess Azula gets a pedicure, showing a close-up of her feet.

Tak and the Power of Juju

Has Jeera who is usually barefoot.

Other series

There are other Nick shows where some character(s) have been seen barefoot such as:

Preschool series

Aquired series