Your parents were about 50 and their ages were starting to catch up with them. Both of your parents had a few wrinkles, were thicker in their body from being a bit less active than when they were younger, and had numerous grey hairs that outnumbered the darker shades their hair had been. So you figured you'd go ahead and mess with the age function a little and figured you'd halve your parents' ages to 25.
Your mother's transformation was astounding as her body shed half of her lifetime. Her hair grew longer and returned to its dark black hair, her chest lifted, her shapeliness became more supple and firm, and the weight of her middle age years was shed. As for Dad, his hair darkened, muscles strengthened, and he generally got a pretty good infusion of youthful vigor. Your parents were shocked to see their youth returned, but after adjusting to the sight seemed to decide it was time to put their younger bodies to good use in having sex.
"What do you say we take off these clothes and have some fun like we did in College?" asked Dad.
"Only if you promise to remember what I taught you since we were this old..." said Mom.
Wishing to not see your parents go at each other, you then decided how much of a buzzkill it would be if your Dad was younger than your Mom and you pressed the button again as the matured stud was about start trying to get his wife to have sex and regress to about 12 and a half where his pecker was just starting to work. Despite being married the now more youthful boy was blushing as he tried to reach for his wife's hand as his adult clothes shrank into just some shorts and a shirt.
"I got younger!" squeaked Dad, who grabbed his throat in shock at the boyish soprano that came out.
"Seems like one of us wasn't done getting younger, Jim."
"I'm just old enough that we could--"
"Jim, I'm not into little boys."
A third halving and the shy boy became a more confident kid of 6 years old who just went to sit in his wife's lap, and then he became three years old and then 1 years old that was closer to 2... press press press and at some point halving months into weeks into days, into hours, into minutes, into seconds left very little for a newborn to regress into. You began wondering if you could push him any younger as you pressed the regression button, and then the little baby being coddled by his wife regressed into his wife's belly.
"Woah..." you whispered as your hand pressed the button again accidentally as your mom's belly shrank back to normal... "umm..." you wondered as suddenly you felt a pressure in your balls. "Crap... Did I just unconceive dad?"