An error popped up on the Chronivac based on the prior transformation. Jeff had made Sharon younger and changed her relationship from mother to older sister of Andy, but the problem was Sharon's mother had died a few years prior, before Andy could have been conceived in this altered timeline. And while the Chronivac could work with people and make them younger and older to balance out changes to reality and timelines--it couldn't raise the dead.
So the Chronivac undid the change of making her Andy's older sister, and reasserted her status as mother to Andy, but then encountered another error--that she was now to you to have a 4 year old son and be sweet sixteen herself. So the Chronivac would either have to make her old enough to be mother to Andy, or make Andy young enough to be her son. The Chronivac's most recent change to make Sharon sixteen tipped the balance over everything else. And so Sharon, unbeknownst to her felt her butt grow a bit, stretch marks appeared on her stomach, and her breasts enlarged just slightly, all of these changes were to prepare for what was to come and reassert the connection between Sharon and Andy. These changes were slight and small enough that Jeff didn't notice them--especially with how Sharon was biting her lip and looking abashed at him.
Meanwhile up in Mikey's room, Andy suddenly was struck by the urge to leave the room and toddle downstairs. Andy stood up, dropping the toy he'd been occupied with until that moment and walked straight for the door and opened it.
"Andy?" asked Mikey, confused as to why his friend was acting the way he was. Mikey watched as his friend toddled out of the room and down the hall to the staircase. Mikey, confused, followed.
Back downstairs Sharon then moved closer to Jeff, and Jeff decided to test the waters by leaning in and giving her a kiss. After a brief moment, the two separated and laughed a little nervously.
"T-that was nice," said Sharon.
"Do you wanna--" started Jeff
"Yes!" And Sharon barrelled into Jeff, pushing his back down onto the couch as the two began to do what any aroused teenagers would do when given a room to themselves: make out.
Andy meanwhile was coming down the steps one at a time, and Mikey stood at the top and watched as his friend continued down the steps without riding down them on his butt like they often had done down the carpeted steps. Mikey followed a few steps behind, curious as to where Andy was going.
Sharon and Jeff were in the process of tearing their clothes off each other as the make out session was getting rather hot and heavy. Jeff reached for a condom from his wallet, but Sharon at that point had unbuckled his belt and pulled down his jeans and underwear in one swift motion which kept him from grabbing his wallet as she grabbed his erect rod and sent him in to a distracting wave of pleasure. By the time Andy had toddled into the living room, Sharon and Jeff were naked and heavy petting was moving into foreplay. It was at this point, that Andy himself started to grow younger and smaller as he first toddled and then started to crawl closer to Sharon. As he grew younger, Andy stepped out of his shorts, leaving an only slightly oversized toddler t-shirt on his body growing smaller with more baby fat accumulating. His hair shrank into his head, becoming shorter and wispy. Soon Andy fell onto the floor on his butt before he leaned forward, his shirt fell off and began to crawl as naked as the day he was born, which he was quickly crawling back to.
Jeff was distracted as Sharon had decided to switch to giving him a blowjob. This left her kneeling on the floor in front of the sofa and leaving her crotch wide open as Andy crawled towards it. Her belly was now starting to round out, preparing itself as a long cord started to emerge from her vagina, seeking out and then connecting with Andy's naval. The moment it did, Andy ceased to be able to crawl as he grew too young to do so and the umbilical cord began to pull him closer and into Sharon. First his feet entered, then his legs, followed by his hips and arms. His shoulders stretched her but it wasn't until his head was pulled in that Sharon really looked to have been stretched out completely before pop, Andy was back in Sharon's womb and she was looking all of nine months pregnant, at which point, Sharon let out a moan and fell back a bit from her knees and onto her butt, pulling her off of the blow job that she had been doing to Jeff.
Mikey meanwhile stared at the entrance to the living room, completely confused at what he just saw
"Babe, are you and the baby all right?" asked Jeff, his own memories being altered to think of Sharon as his long-term girlfriend and her pregnant with his kid.
Sharon took a few deep breaths, and placed her hand on her belly, which shrunk a little from nine months to eight.
"Yes, I felt him kick is all," said Sharon as she took Jeff's hand and placed them on her seven month extended belly.
"Let me help you up," insisted Jeff, and he helped Sharon as she left her third trimester for her second and helped her to sit on the couch.
"I'm starting to get too big to do much, Jeff" said Sharon as her belly shrank to five months along.
"But not too big for me to do something," said Jeff as he snuck his hand down her thigh and gently brushed it, causing Sharon to shudder. This led quickly to Jeff kneeling before Sharon and kissing her until his mouth began to probe her depths. Sharon grasped the couch, and all the while her belly shrank until she hardly looked pregnant at all. Her stretch marks vanished, and her breasts were no longer quite so big, at which point she grabbed Jeff and pulled him out of her.
"Enough foreplay, I'm ready."
Jeff didn't hesitate as he joined her on the couch before being pushed down as Sharon lowered herself onto his fully erect penis and began to ride him. Their rhythmic humping soon came in sync with each other until both let out a scream as Andy went from a fertilized egg to an unfertilized one as Jeff penis sucked back the sperm that had made Andy. It took but a few moments for them to catch their breath before they were back at it. Mikey watch fascinated, confused, and curious from his vantage point near the entrance of the room as Jeff and Sharon reconceived Andy. Andy's previous clothes vanished as the Chronivac finished fixing the error. To his young mind, with the rearranging realities Jeff had left Mikey and his two friends upstairs to play, and when Sharon had come, Jeff had left them alone, and Mikey, curious, came downstairs when he had heard the moaning.