you need to put them in a pet house. And there's an option to 'try for puppies' or something like it. Just like you do with sims. The only difference is where they are going to do it
and if I remember correctly it's one of the human sims that has to be selected to click on the pet house and send the other pet to make puppies. I'm sorry it's kinda vague, I don't really like pets in my game they annoy me. But I think that it's right if I remember correctly. I just did it once
