Try 1 finger.

Carl was enjoying circling Steffi's ass hole with his finger. Her butt would contract slightly as he spiralled his index finger to the centre and he thought he could hear Steffi breath in slightly as he did it. She was ready.

Carl spiralled his index finger into the centre of her rosebud, then pushed gently. He let her asshole open up and pressed his index finger into her.

"Ohh.h...." Steffi yelped.

He had gotten to the first knuckle. He pulled out slightly so that just the tip of his finger was touching her asshole. He then pushed in again

"Ohhh..aahhh..." Steffi moaned as he pushed in slightly more, this time to the second knuckle. Steffi had tensed up, but Carl rubbed her ass cheeks to relax her in this position. He couldn't believe he had his finger halfway up his step-sisters ass.

"I'm going to push it all the way in now...." Carl said as he squeezed into her asshole down to his third knuckle.

"Oh oh oh..." Steffi yelped.

"Are you OK?" Carl said, rubbing her ass.

"Yeah, it feels a bit funny though... I think you could probably put the thermometer in now." Steffi whispered. She looked a bit flushed and Carl wondered whether he could convince her to play a little more.