It was early morning, Jaffar walks into Aden's bedroom. He sees his father looks shorter, and sees the open box. He decides to investigate.
Jaffar had originally come in to nag his father for a dog. There was a pet show at school, and everyone was bringing something. His father had told him to go catch a cricket or frog, but no dogs, as Aden had fur allergies.
The CYOC kit was pretty self-explanatory, and Jaffar had soon found the right bottle. He grinned as he filled the eye dropper. Then he held it over his Aden's open snoring mouth, and let one drop fall. He frowned, his father was big, and besides the pills could reverse any changes. He emptied the contents of the eye dropper, refilled, emptied it, and refilled again. About half way through emptying the third eyedropper full of changing solution, Jaffar noticed his father was getting hairier. He grinned, and emptied the eyedropper.
Aden in his sleep stretched, and Jaffar grinned as his father's arms and legs began to reshape. His fingers and toes were clearing no longer human. A bright red conical cock emerged from Aden's boxer shorts before he rolled over on his side. Jaffar could see the tail growing inside the boxers, and slid down the waistband to allow it to grow free. He removed the boxers, since dogs don't need clothing. He noticed his father's mass seemed to be shrinking too, as he changed into a canine.
Holding the boxers, Jaffar had another idea. He took a drop himself and said, "I wanna be grown up."
Soon he was shooting up from less than 4 feet to over six feet. His pajamas hung in taters around his limbs. He shucked them off, and put on Aden's boxers. His new adult body, was also having some adult ideas.
"Father may not be too happy about being a dog. There was something about mental changes in that manual, maybe I can make him happy and obedient, too." He reread the manual as Aden's skull reshaped projecting his jaw and nose outward and moving his ears to the top of his head.