Hm… if I remember right, it is planned that you will see some sort of “option screen” once you start a new game. There you should be able to activate the pet(s) you want to have in the game, i.e. if you should get more than one from Kickstarter, you can decide if you want them all in the game or just some / one. Regarding the dragon whelp… there was a hint that this might need another way of “activation”, like a hidden key you need to enter somewhere.
I guess that your activation code will determine if you are a backer from Kickstarter or not, so the options related to the pets can be restricted this way.
For me that would work perfectly.
Also I think that it was mentioned that your pets will run around through your city. I could imagine that if they meet an idle NPC, they might start interacting… would be nice at least.
Just like everything else… still some speculation behind 
.