"This is pretty much the typical Tuesday morning," McGehee said as he speaks with Mack's therapists who have worked with the boy for the past three years. "Sometimes we'll all come over here with Mack and then grab lunch before I head to the park."
In a season McGehee has gone through some of the toughest times of his professional career, off the field, his family has helped keep him upbeat.
The strides Mack is making in therapy help McGehee see the simple pleasures in life. Mack is improving his balance and core strength, has replaced his walker with leg braces and can even swing a baseball bat and make contact without falling over.
"He used to be a lot more wobbly," Mack's physical therapist said. "We try to improve his hip strength and core, and he's come a long way."
At home it's easy for McGehee to step away from the game as his children expect the same dad to come walking through the front door. The moments father and son share on the field before games, when Mack runs around in the outfield, remind Casey that like most parents, he can't let a bad day at work carry over to his personal life.
"What's going on at the park I have to leave at the park," he said. "My drive in, I use to get myself ready and the drive home to decompress or whatever. I don't always do the greatest job of it, but the kids and [wife] Sarah, they shouldn't have to suffer if I had a bad day. Just like any parent who's had a bad day at their job."
A little thoughtfulness goes a long way
It's easy to see why Mack's become a fan favorite. After throwing out the first pitch during a Brewers game two years ago, his story struck a chord with the fans. The fan base has embraced the McGehees and their involvement with United Cerebral Palsy, and McGehee said he still receives more questions from fans about Mack than anything else.
It probably helped that the boy has an infectious smile and can rattle off the results of the sixth-inning sausage race with unparalleled enthusiasm.
On this day, Sarah is home sick, so McGehee watches Cooper pull herself up on to any imaginable surface, while Mack works in another room to complete his hour of occupational therapy.
The boy walks into the waiting room and gives his sister a kiss on the cheek before telling his dad about the letters he wrote. Making a karate chop motion with his hands, Mack explains how he enjoys writing the letter "K" and waits for his physical therapist.
His blue eyes widen as he claps with Cooper, who fusses over her brother giving her so much attention. Even Mack's thoughts are well composed for a boy his age as he likes to take his time and think before giving any answer.
"Thoughtful, I guess, would be the word for him," McGehee said. "He's a very thoughtful boy. And he always wants to know why. The stuff he picks up on sometimes amazes us."
Mack understands that his dad is a big league ballplayer and can also sense when something isn't right. Before the All-Star break, McGehee was pressing to try to find his swing and was benched for a few days during the Minnesota series. Mack knew something was up when his dad wasn't on the field and wanted to comfort him.
"The little guy comes up to me one day with his teddy bear and wants me to hold it because it makes him feel better," McGehee said. "For that, it makes it tough."
"What about my teddy bear?" the boy asks while McGehee stands next to a trampoline in the physical-therapy room and retells the story.
"Remember when you gave me your teddy bear to hold and it was very thoughtful of you?" McGehee said.
And then Mack, in typical 4-year-old fashion, has already moved on to wonder about more pressing issues.
"Yeah, I remember," Mack said. "But Dad, can we go to lunch after this?"
McGehee chuckles and nods his head. It's easy to see why baseball is the furthest thing from his mind when Mack is around.
Sometimes you just forget
The brightly colored walls inside the physical-therapy room used to be a place where the realities of Mack's disability hit home for McGehee.
Seeing his son struggle to complete ordinary tasks, like walking and balancing, were initially hard for McGehee to come to grips with. Watching other children with disabilities enter the center and get frustrated when they were having a bad day took a while for McGehee to adjust to.
"They'd be yelling and crying, and they'd think it's the end of the world just because they couldn't do something," he recalled. "That was tough for me to get used to at first."
On this day, things are fairly calm at New Berlin. Mack proceeds through his exercises in a room that is complete with mats and ramps, balls and ropes, a slide and a trampoline. Aside from the occasional dart toward the ball pit, he's reminded that every exercise has a purpose and that he's here for work and not play.
"Sometimes you forget that he has brain damage," McGehee said as Mack holds onto a green rope and walks on a treadmill. "It's tough for us to see the big developments he makes because we're with him all the time. But for his therapists here who don't see him for a few months at a time in the offseason, they notice it."
New Berlin was the first place the family tried, and having the same team of therapists with Mack for the past three years has helped the boy grow independent, too. McGehee said he and Sarah aren't sure when it happened, but Mack now strolls from room to room listening to his therapists while his mother and father can either wait in the lobby or run errands.
"I don't want to hear any squeaky mice, Mack. You can do it, pick those feet up," his therapist said as he lifts his braced legs up off the belt and marches forward.
McGehee watches from the side and after the treadmill, Mack is led to his next exercise, where he tells his dad he lifts weights just like him.
"Wow, Mack, you're so strong," McGehee said while the boy tugs at the rope for an extra rep.
"No, I'm not," Mack said as he smiles. "You're stronger."
This is our obstacle
Inside the clubhouse, Mack is just like every other player's child. He wears his dad's No. 14 jersey, enjoys going out on the field before games to play catch and talks with his dad's teammates.
"Hey, dude, I saw you out there in the sausage race the other day. Did you have fun?" All-Star left fielder Ryan Braun asks Mack as the boy shows Braun his baseball glove.
"I was Bratwurst and I beat my dad," Mack said as he talks about his experience in the junior sausage relay race where McGehee held his hand and ran with him.
Braun tries the glove on and shows Mack how he needs to break it in before the boy heads out to the field. The little details of the game aren't lost on the 4-year-old.
Mack likes to imitate Braun's warmup swing, and at home he likes to have his parents turn up the music and let him run out of the bedroom as he pretends he's coming out of the bullpen like Brewers closer John Axford.
"I don't wake up in the morning and think, 'Oh, my son has a disability, what's going to happen today'" McGehee said. "Every person on this team has to deal with stuff too, and for our family, this is just the obstacle that we have to deal with."
Seeing Mack lift his feet up off the ground as he jumps five consecutive times on a trampoline during his therapy session is just one of the small victories McGehee is glad he's around to witness. Father and son jump alongside each other as Mack holds on to McGehee's leg and the youngster can't stop smiling and laughing.
"Whether there are tough times or things are going good, he's my guy," McGehee said. "No matter what."