I stroke my nieces stomach when she cuddles up during a movie, it's a thing that developed over time and we now do every time. Sometimes bare belly as well.
I know it gets her really really horny because after such moment she tends to take a pee, but I followed her and listened at the bathroom door, I heard definite schlicking sounds and sighs/moans.
It's something we both enjoy without ever talking about it. I'm also sure she would let me access her pussy, one time I 'accidentally' went beyond the band of her panties but decided to stop because of the trouble I could get in.