Zack decided to change his own room.
With a thought, Zack willed his bed to become larger, king sized. He changed his wallpaper from the childish style it had been before to a solid green. He went around his room, transforming everything... until an idea hit him. Did other people notice the changes?
"I would need a test subject," he thought. He did not pause for long before he realized he already had a suitable guinea pig, his sister.
Zack returned to his sister's room, where Susan was still sitting where he had left her, babbling happily. With one wish, she returned to her previous age. She was still sitting on the floor for a moment before she thought to get up.
"What do you want, dweeb?" she asked, sitting down at her desk, obviously none the wiser about her transformation.
"Nothing... but, doesn't something seem odd about your room?" Zack asked, trying to be nonchalant.
"Shut up, dork, you know it's always been like this." She stared at him accusingly. "Why? Did you take something? If you did..."
"No! No! I didn't!" He quickly replied. That answered a couple questions for him, that the changes went unnoticed, whether to a person or their surroundings, but there was one more question that needed answering. A quick wish solved that.
"Well, then, if you have nothing to say, then leave." She stood up, revealing her clothing fully. Instead of the t-shirt and pajama pants she had been wearing moments earlier, she now wore a much shorter t-shirt, ending just below her belly button, and a diaper. "I've got to change myself."