He decided to see who he came across first, and have that be his target. "This could be fun, depending on who I get!" So, he walked out of his room, and started looking around.
After a few rooms, the first one he saw was his younger brother. Peeking in the room, him and Izzie were playing together in Izzie's room, with stuffed animals spread out. He had his decision, and while he could've backed out, he decided to stick with it. "I just need good timing."
He sat there outside the door for a few minutes, trying to stay out of sight. He knew he found his chance when he heard Izzie speak up. "Sorry, Maxie.. I hafta go potty." He watched as Izzie stood up, and went into the bathroom, leaving Max alone. "Now's my chance."
Jeff quickly took his clothes off, hiding them in a nearby doorway. Sneaking into the room, Jeff made sure the bathroom door was closed before walking to his younger brother. Max was focused on his toys, so he didn't even notice when Jeff pulled back his pants, and jumped in.
With his position, he hopped right in. He slid in surprisingly easily, despite being a lot bigger than Max. The waistband of the diaper closed behind him, and he was fully inside. With his eyes closed, he adjusted his position, eventually feeling Max's foreskin in front of him.
Going into this, he thought he'd regret his decision once he saw Max. But, Jeff finds it surprisingly comfortable in there; His legs are soft, and he hasn't smelled anything yet, although his nose is right against Max's crotch. He almost felt as though he could fall asleep here.