He took a left-handed-swinging approach while mimicking his father Tony Gwynn, the Hall of Fame outfielder known as "Mr. Padre."
Tony Jr. later learned to write as a right-hander and developed an effective right-handed shot as a skilled high school basketball player.
But the left-handed swing somehow stuck -- perhaps an indication of the continual subtle influence his father would have on his progression to the Major Leagues.
"He never really said anything about baseball," Tony Jr. said of his father. "He didn't want me to feel pressure of having to play. I think that's why I love the game as much as I do now. I was able to establish a love for it by myself."
Tony Jr. spent five years with the Milwaukee Brewers organization before making his way to 19 Tony Gwynn Drive, the address of the Padres' stadium in downtown San Diego.
The Padres traded outfielder Jody Gerut in late May to acquire Gwynn, who was playing for Triple-A Nashville.
Tony Jr. was in Portland with Nashville on May 21, digging into a hearty breakfast plate of eggs, bacon and pancakes when his father called.
The elder Gwynn recounts the conversation with a wide grin and elaborate theatrics.
"I said, 'Did anyone talk to you about anything?'" And he said, 'No. Talk to me about what?'" Gwynn said. "I said, 'That you've been traded." He's like, 'Traded to who?' And I said, 'The PAAAAAADDDRREEESSSS!'"
Since that day, the elder Gwynn hasn't been able to hide his jubilance or emotional investment in his son's performance.
"I've been on cloud nine," he said.
His new boisterous cheering habits might seem odd, considering Gwynn coached Tony Jr. for a year at San Diego State and has watched him play both baseball and basketball for years.
"The other night, he got a hit and I stood up and shouted, 'Yeah! That's my boy!'" he said. "It's so un-Tony Gwynn-like. I'm losing my composure day by day. I've gotta get a grip."
Gwynn said he's always tried to take a supportive rather than critical role as an athlete's parent.
"It's tough being the son of a guy in a town that people know," Gwynn said. "When he played basketball, I'd sit in the stands and take my little video camera and video tape the whole game."
Many have questioned the pressure involved in the trade for Tony Jr. Will the younger Gwynn be crushed by the weight of unrealistic expectations?
And how does Tony Jr. feel when he turns onto Tony Gwynn Dr.?
"Like it's a regular street," he said. "I don't even really notice it. I played in a stadium that was named after my father in college. It's just like putting your pants on. You just do it, and you move on."
Tony Jr. chose to wear No. 18 for the Padres, one shy of his father's No. 19.
"He always wanted to establish his own identity," the elder Gwynn said. "People were asking me, would I let him wear 19 if he had wanted to. Yeah, I would have.
"But I know he doesn't want to. He wants his own number. He does things differently. That's fine with me."
Growing up as the son of a San Diego legend had its perks for Tony Jr., although there were times he strove for a sense of normalcy. He attributes his current "deal with it and get over it" philosophy to early exposure to the critics.
"When you're playing Little League baseball at the age of 9, you really don't want to be compared to your dad at that age," Tony Jr. said. "You're just out there playing baseball."
As a child, Tony Jr. wasn't a regular in the Padres' clubhouse. His fondest childhood memories weren't baseball related, instead involving trips to the movie theater with his dad "before he could go outside without it being a big deal."
"When I started first grade, it's starts to dawn on you a little bit that, 'Hey, my dad is a little special, and he's doing something a little different than everybody else's father,'" Tony Jr. said. "But that didn't interfere with our family relationship. He always was dad at home. He was Tony Gwynn on the field."
Once Tony Jr. reached the age of 10, his father decided to bring him on the road for some additional bonding time. He got a little more than he anticipated.
"We'd have a room with twin beds in it, and he would drive me crazy every night, watching movies, ordering room service," the elder Gwynn said. "We'd go on the road, and I'd have to pay double clubhouse dues because he'd eat so much food."
Now that Tony Jr. is married with two daughters under the age of 2, Gwynn said he will treasure to chance to watch his son mature and grandchildren grow up in the shadows of PETCO Park.
Days before Father's Day, Tony Jr. sat by his locker, pondering a significant gift for his dad.
"He's one of the toughest people to shop for," he said. "I've gotten him ties, pajamas and pen sets. He has absolutely everything."
Hearing word that his son was struggling for gift ideas, the elder Gwynn chuckled and shrugged.
"That's fine. It can't get much better than it is right now," he said. "My son is here playing in a ballpark that his dad didn't get a chance to play in. .... But I'd like to think maybe I had a little something to do with this place getting built. I'm glad he's getting the chance."