He heard Amy and Kyle giggling in the kitchen. He took a deep breath and selected AGE.
He could instantly feel something different. He was getting older! He felt himself grow bigger, getting muscles on his chest. His red 'Spider-Man' t-shirt changed into a sleevless shirt and the shorts that only ended at his kness grew down to his calves.
He heard someone running into the computer room. He turned and saw a ten-year-old Amy enter. Her flower bikini had become a two piece bathing suit that little girls wore. Her mother was wide open as she stared at Max. "What's going on?"
"We switched ages," Max said, "I used this computer program so you could see what its like to be the little sister."
"YOU did this?"
"Yup, but I think ten years is too old for you." He turned back and made Amy's age regress by five years.
"What?" Amy gasped, "Max, what are.." She started to shrink even more. Any developing breasts she had completly disappeared. Her two piece bathing suit turned into a once piece and her hair changed into pigtails. She looked at herself. "What did you do to me?"
Max got up and towered over her. "Now you're going to find out what it's like to be the younger sibling."
Kyle walked into the room. "Hey man," he said to Max, "What are you doing here? I thought we were going swimming outside?"
"Uh, yeah, I'll be right there."
Kyle looked at Amy. "You're kid sister's not comming too, is she?"
"She can," he said, "But she has to stay in the shallow end. I'll be right out."
Kyle nodded and walked back out of the room. Max grinned at Amy. "See that? He's my friend now, you're just a little pest that gets in the way."
Amy felt herself start to cry. "You're so mean!"
"Shut up!" Max shouted, "I might change you back, if you play along." He reached over and lifted her over her shoulder, "Now come on."
He brought her outside to their swimming pool. He made her sit inside of a inflated inner tube. "Now, I'm going to have fun with MY friend. Don't bother us, you're just so annyoing!" He walked away.