Jack Backe, joined by his family, was honored Wednesday by the Chicago Cubs for the big accomplishment.
Backe was given a tour of Wrigley Field, met Kyle Schwarber and Addison Russell, and then delivered the starting lineup to the umpire.
Backe's design entry was one of about 6,000 submitted to the Starlight Children's Foundation competition.
His hospital gown design honors his little sister, Everly "Evy" Backe, who is just eight months old, but had three heart surgeries because of a congenital heart defect.
Outside of Wrigley Field, Jack's jaw dropped as he learns the news.
"It's your gown, buddy! And now Everly is going to get to wear it and so many other kids all across the country are going to get to wear it, too," said Chris Helfrich, CEO Starlight Children's Foundation.
Jack met players and got a behind-the-scenes tour of the ballpark.
"I'm so excited!" Jack exclaimed when he learned the news he'd won.
Jack designed a gown that his sister and other kids would want to wear and focused on the heart.
"One is for Ev, one is for my three pets, they share one, and one is for mom and one is for dad," Jack said pointing to the four hearts on the gown.
The foundation will make and give away 30,000 of Jack's hospital gowns to children around the country.
"I'm just so proud of how well he's done. And it's because he wants to make a difference for his sister. And I guess I'm kind of shocked at his age how much he cares," said Jack's mom, Lauren Backe.
Baby Everly and the Backe family still have a long road ahead of them.
"I'm not looking forward to the next surgery, but I know that it has to be done because it's going to help her be better," Lauren Backe said. "But this makes it a little more tolerable."