Petpet Park was released as a training and social area for Neopia's Petpets. It seems to have been created through the magic of the Wand of Wishing, though the exact details of how are still unknown.
During the beta testing period, a lot of the original Neopet characters that appeared in the introductory Mini-Plot were replaced by Petpet characters. It is unclear what future role, if any, the Neopet characters will have in Petpet Park. A full list of the Neopet characters can be found in the Petpet Protection League Hub.