Drake opened his eyes to see that he'd selected his actual father, and he felt a little glee surge in him as he entered in Tim's old age of 10 years old for Dad to become. Dad wouldn't become Timmy--Drake didn't want to do that--instead he'd become a new twin for Tommy to twin with while Tim took a turn at being Dad for a little bit.
Dad, or Tad as his actual first name is, fumbled with the front door as he tried not to put down the bags, which he managed to do as he brought the bags into the house and then pushed the front door shut with his foot. As he walked across the living room the transformation started from what Drake could tell.
With each step, Tad's belly shrank and his muscles grew a little bit. Pretty soon a rather hairy and fit young man was putting the bags easily down on the dining room table he'd been aiming for. As he placed each bag however, some of the hirsuteness of that young man started to fade as he began to look more fresh-faced and smoother as burly blond hairs began to retract and muscles shrank a bit. By the time one arm was free of bags, Tad looked like a fresh-faced college freshman.
The transformation continued as he unloaded the rest of the bags, muscles shrank further, hair thinned out and shrank back into Tad's skin, and his height and build took hits as he thinned out, shrank, and pulled in on himself. Pants fell to the floor, revealing a hard-on that was the only thing keeping his boxers up and soon became the sole focus of the young teenager's attentions as he dropped the last two bags in his hands and pulled down his boxers in favor of fisting himself.
As soon as he started he was practically over. He came rather quickly, and shortly afterwards lost any and all signs of puberty as Tad shrank to the ten year old boy he'd been programed to transform into. Tad looked at the pile of clothes he had around him, the oversized t-shirt he was wearing being the only thing to preserve any semblance of modesty. Tad left what few bags he hadn't put on the dining room table on the floor and shuffled over to the mirror in the living room.
"Why am I wearing Dad's old t-shirt?" asked the towheaded and innocent eyed Tad as he pulled at the baggy shirt that fit him like an oversized t-shirt that some children and girls slept in for pajamas.
Drake smiled at himself for the transformation of his Dad that would preserve the ruse of Timmy being Dad for now. Tommy and Tad were now "the twins".