"His mom asked me what position I played, and he looked at her like she was crazy," Johnson said. "He was upset and embarrassed that she didn't know what position I played. He looked at her, and he said, 'He plays center field.'"
Jack was one of several star-struck kids who met Cubs Ryan Dempster, Michael Wuertz, Mike Fontenot and Johnson at the University of Chicago Comer Children's Hospital on Tuesday morning.
The players signed autographs and dispersed Cubs hats. More importantly, they put smiles on the patients' faces.
"You come here, and you think back when you were a kid seeing a lot of them," Fontenot said. "We saw a kid that was burned today, and some other ones that are going through a tough time. It's good to come out here and talk to them, let them know that everything is going to be all right. Once you see the smiles on the faces, it really makes you feel good."
The players took part in a question-and-answer session with some of the children to start the day. The most frequent inquiry was what position each played. Not everyone knew the Cubs roster as well as Jack.
The Cubs had their fun, too, posing for pictures and urging the kids to turn on ESPN on Tuesday night to watch the game against the Dodgers.
The experience made Dempster thankful for the health of his son, Brady, who turns 2 Wednesday.
"One kid was a really big basketball fan, and I said, 'Oh, a Bulls fan.'" Dempster said. "He said, 'No way.' That was pretty funny. Kids basically telling their parents to beat it, you know, I'm busy talking to some athletes right now. It was a lot of fun. I had a really good time."
Jack may have been the biggest Cubs fan, making Tuesday's visit particularly memorable. As for Jack's mom? She might need to brush up on her Cubs knowledge.
"I could tell he was upset with his mom," Johnson said. "She'll get over it."
Nick Zaccardi is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.