Jeff had an idea, and decided to go for it. "This could either be fun, or backfire horribly." He minimized the Chronivac window, promtly leaving his room as he headed to where he knew his youngest sister, May, would be.
Entering the room, having avoided his other sister, he walked over to where she was playing. He picked her up, and set her somewhere more hidden from sight. He reached down and pulled her skirt up, before pulling her full diaper down, his sister looking cute and confused. He was about to enter, before deciding to do something else. "It may be a bit tight right now, and It'll be where I'm located soon anyways..."
He pulled his pants down, and shoved his penis into May's small vagina, covering her mouth to prevent her from screaming. He sat there for a few seconds, pulling in and out as best as he could to open it up a bit, before pulling back out entirely as his sister looked like she wanted to cry. "Now it should be time"
He put her onto the ground, sitting right behind her. He took in the view for a second, before the stench of her diaper got him; "I'll have to deal with that first, it's too much!"
Trying to go fast, he pulled her diaper all the way off, disposing of it and clearing the stink; He didn't grab an extra, as he didn't know how to put one on, however. He laid her down on her stomach, and positioned his feet near her vaginal opening. "Alright, it's time..."
He pulled her backward, his feet going inside her tiny vagina; He could tell she was in pain, but he continued on, pulling her more. After a bit of pulling, the Chronivac kicked in, regressing him down and shrinking him as he entered position; He entered a bit further, having his penis stick out a bit.
He adjusted his position as best as he could, having his baby sister now sitting on him. Trying to get into a better spot, he lifted her as high as he could, crawling under so that he was sticking out in front of her. He could only chuckle at the thought of this look; Him at a young age laying on his chest, and right behind his small penis is the vagina of his younger sister, as he was between her legs. May's labia was soft, comforting his crotch and encasing his penis almost entirely.
Pushing himself up, he got his position to where - Aside from his lack of legs - it appeared as if he was sitting between her legs. At that point, he waited a bit...