In her ass

You shake up the can of whipped cream, before sticking the nozzle in Mia's surprised asshole and spraying. The foamy cream sprays as far as it can into her ass. The moment you pull the nozzle some of the cream comes spraying out of her ass, most likely involuntarily.

"Oh fuck daddy. Is this what you meant by dessert?" She giggles as she looks at the whipped cream flowing out of her ass.

"It is now. Why don't you lick it up slut."

Tracy lowers her mouth to her sister's ass and sticks her tongue out. She then licks up the cream popping out of her ass, before sticking her tongue as far into her sister's ass to slurp up the whipped cream. Mia tries to help her out, and pushes the cream out as best she can. This causes the cream to come spraying out of her ass and onto her sister's face. The three of you simply laugh as Tracy's face is covered with the whipped cream.

"Why don't you help clean up the mess you made whore."

"Yes daddy."

Mia put's her hand to Tracy's chin and brings her head up to her own, before licking up the cream that she sprayed out of her ass. Once she's licked it all up, the two of them start making out once again. Whilst they're doing this, you grab a banana from the fruit bowl and bring it over. You then spray some more whipped cream in Mia's ass, causing her to gasp into her sister's mouth. Then once the whipped cream starts overflowing out of her ass, you pull the can away before bringing the banana to her ass. You then push the banana up against her hole, causing Mia's eyes to open wide whilst she makes out with her sister and look down at what you're doing. You then force the banana into her ass, using it to fuck the whipped cream deeper in.