And "kitten" is "kissanpentu" which literally means "a cat's juvenile". Puppy then again is "koiranpentu" which means "a dog's juvenile", so we take the word pentu and add the animal word in front of it to specify which specie's baby it is.
Sillä on kaksi kissanpentua. - This could indeed be the right answer so the duo translation isn't correct if we're exact. But here "sillä" already points out that we know the animal we talk about. Pentu alone is then the normal way to say it.