Have a mate of the opposite gender. As a male, give your mate a second pink tulip, then say yes to try for kits. Give them a third tulip and if they don't say anything, your try for kits was unsuccesful. If they say: "Oh! Honey... in case you didn't know, I'm expecting kits!" It'll take around five minutes for the kits to be born. They'll show up in that clan's nursery. For a female, keep trying for kits with your mate until the cat icon shows up on your screen.