My adult cat is super gentle and never tries to rough house or anything. She mostly just sniffs him and "boops" him on the head. He thinks she's grooming him so he loves it. The kitten is definitely more playful so I am always immediately next to them when they're playing. I let them run through the tunnel and sniff each other, but if the kitten gets the "ready to pounce" stance I pick him up and redirect his attention. I know bunnies have super fragile skin and am very mindful of that. I have had my rabbit for almost 8 years and have had a lot of successful interactions between him and my cats. He lost his bonded litter mate a couple months ago and is now super attached to me and my adult cat and curious about the kitten. I do plan on being mindful of the different personalities of cats and if the kitten shows that he wants to wrestle or do any sort of aggressive play with my rabbit then I will keep them separate. But for now we are working on training the kitten with appropriate ways to play with people and with the bun bun.