I know you can only make kittens/puppies in CAS on the Console versions of TS3 Pets but I still know from experience you can put puppies and kittens into CAS two ways
1. download a puppy/kitten to your CAS bin and select them from there, then make edits as you want.
2. Use Nraas' master-controller and "edit in cas" on an adopted puppy/kitten in game, edit them as you want from there on.