I'm currently working on pets to include with the new set of heroes, and they're raised some questions and quandaries! Simply put, pets can work like extra heroes (with all of the usual actions and abilities) or they can work as an extension of the hero that they 'belong' to.
Here's an example pet that would be an extension of the hero it belongs to:
The reason for the difference between pets with full sets of actions and those that are extensions of their heroes is to do with the 'action economy'. If the heroes of some players have pets and others don't have pets, then the players whose heroes do have pets will have much more stuff (more actions) they can do on their turn than the other players. This will make the other players sad. Which makes me sad.
However, if solo kids are playing with pets, then they would probably prefer to have a full set of actions for both their heroes and their pets...
Check out Hero Kids and its adventures at DriveThruRPG:
Hero Forge Games at DriveThruRPG