You watched as your older brother zoomed around his room getting ready to go out with his hero friends. You were only 10, and you had your own friends, but damn, his friends looked so much cooler.
What you've picked up through your amazing detective skills is that Wally can't register weight when he runs. So, when he took off to meet Dick, he failed to notice the 54 pounds on his back. It wasn't until Dick actually pointed it out did he realize.
"I didn't realize you were bringing your little sister."
"What-"
He turned around. Then again, continuing until he realized you were on his back. He called your name scoldingly. You weren't trying to get his superhero identity thing in trouble. You just wanted to hang out with the big kids.
"What're you doing?!"