Ty spotted another boy in the aisles, looking at jockstraps. He must be doing a sport, he thought. Oh no matter, Ty could help him with that! Ty deviously wished that once the boy tried on the jockstrap, his cock and balls would grow until the jockstrap reached its absolute limit! The boy eventually selected the medium "enhancement" size (how fitting, Ty thought) and headed to the change rooms, with Ty in tow. Ty was curious how this would turn out at this point so he wished to be invisible and followed.
Closing the door, the boy stripped down and Ty saw that the boy had fairly normal genitals, maybe on the small side, although not that small. Ty estimated around 2.5 inches soft, with grape-sized balls. Either way, he was about to do much better. Ty silently wished to be able to see through the garment in order to see better. He also wished to know what the boy's name was and what he was thinking and feeling, because Ty wanted to know.
The boy slipped the underwear over his equipment and stared in the mirror. He smiled for a moment, then groaned in pleasure. Ty spotted movement inside the jock as his pouch began to slowly fill out. It was a small improvement, but Ty estimated he was now around 3 inches soft. He knew it would continue growing.
The boy looked down and his eyes went wide as he saw that the pouch was still inflating. Curiously, he stuck a hand inside and felt his cock growing in his hands. His eyes lit up in joy and he danced a little, the pouch jostling around just slightly more than it would have.
Quickly, the boy pulled up his shorts, which concealed the bulge for now. For now, the front remained mostly flat. The boy quickly ran back out to the underwear shelf, closely followed by Ty who was trying to conceal his laughter. The boy picked out the largest size available of briefs, boxers and of course a jockstrap, the XL ("meant for extremely big men" it said on the package) and hurried back to the change room as fast as he could. He wanted to support his new member, but he didn't know how big it would become. Ty could see through his shorts and saw that his cock was still expanding and pushing the material farther out.
Suddenly, Ty had a funny idea. He wished all of the clothing stalls were occupied. He wanted to see how the boy would react to growing with his clothes on in a more public area.
Back inside the changing room, the boy ran into a problem! All of the stalls were occupied now - someone had entered while he was away and he would now have to wait. At first he relaxed, but then the boy stiffened as he realized - he was still growing. Looking down, he confirmed that whereas before his shorts had been mostly flat, he was now showing a small hump at the front.
Nervously, the boy bounced on his feet, checking his bulge every few seconds. Each time, it seemed to be just a little larger. Glancing around to make sure nobody was watching, the boy stuck a hand inside the jock and rearranged his cock to point straight up, and be less obvious. A wave of excitement ran through him when he felt the new thickness of his cock through the material.
Satisfied that the bulge was less obvious, the boy relaxed a bit and pulled out his phone, scrolling absentmindedly through his feed and ignoring the tingles coming from his groin. Ty could see that although it was less obvious, his cock was still growing. So he let the boy just wait, knowing that all of the stalls would remain occupied until he said so.
After a minute or so, the boy looked around nervously and then down. He saw that the bulge was still growing, and that it was larger now. Once again, the boy attempted to rearrange his cock, but he was out of options - his cock was starting to become too big to hide.
Finally, Ty graciously allowed a stall to open and the boy slipped inside, hurriedly placing his stuff down on the chair before turning around to the mirror....
"Holy shit" the boy whispered. The front of his shorts were now unmistakably bulging, much more than any kid his age should. He hurriedly pulled off the shorts. Now with the clothes removed, Ty could get a good look at the boy. The jockstrap was stretched to its absolute limit, the fabric turned sheer in the face of the stress of the enormous cock behind it. Just then, the tingling sensation stopped for the boy, the jockstrap having reached its absolute limit.
Almost as if in a trance, the boy pulled off the jockstrap. Hanging down from his groin was a thick nine incher, completely soft and quite heavy. Behind it, two tennis-ball-sized testicles hung low. It looked out of place on the 13 year old's scrawny body.
The boy quickly pulled on the sweatpants, which didn't completely hide the bulge, and went out to the front to pay for them, running off quickly. Ty just smiled.