Colin Kaepernick was raised by cheeseheads.

His grandparents were Green Bay Packers fans since the days of Vince Lombardi, and his aunts and uncles had season tickets at Lambeau Field.

His parents? Even after the Wisconsin natives moved to Turlock when Colin was 4, they raised him with the Pack mentality. After church, they'd change into their other Sunday best (green and gold Packers gear) and head off to a sports bar to cheer on Brett Favre.

But on Sunday, the Kaepernicks would love nothing more than to see Colin trample all over their once-sacred ground. The quarterback makes his first career start at Lambeau Field, where the 49ers (12-4) open the playoffs against the Packers (8-7-1) in an NFC wild-card game.

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Five-year-old Colin Kaepernick, right, poses outside Lambeau Field in Green Bay, Wis., with cousin Brett Kaepernick. Both boys are wearing Brett Favre jerseys. (Courtesy Kaepernick Family)

Kaepernick is here, in part, because of his upbringing.

"Just watching Brett Favre play every Sunday really makes the passion for the game grow on you," the quarterback once said.

There's a snapshot of Kaepernick as a kid outside Lambeau Field, posing in matching No. 4 jerseys with his cousin. Even as a Californian, his family vacations as a kid included trips back to the Packers Hall of Fame and to the team's training camp.

It fueled his dreams. By the time Colin was in fourth grade, he wrote a letter to himself for a class assignment that said, in part: "I hope I go to a good college in football then go to the pros and play on the niners or the packers even if they aren't good in seven years."

To his relatives, many of whom still live within a half-hour of Green Bay, this is an almost surreal turn of events.

"I'm going to be so excited, I'm not even thinking about the cold," said Kathy Algiers, Colin's aunt, who lives in Appleton, Wis.

The forecast for Sunday calls for 2 degrees at kickoff, with a wind chill factor of minus-20.

Or, as Colin's grandfather might call it, "balmy." Edgar Algiers was in the Lambeau Field stands for the game dubbed "The Ice Bowl," the coldest game in NFL history, when Bart Starr led the Packers past the Dallas Cowboys in 1967. That game featured minus-40-degree wind chill temperatures -- cold enough to freeze your tundra off.

Edgar won't be at Sunday's game (he's scheduled for back surgery soon), but he was on hand for Kaepernick's one-play cameo there on Sept. 9, 2012. Serving as the backup quarterback behind Alex Smith, Kaepernick trotted onto the field with a few seconds left before halftime.

Rick Kaepernick, the quarterback's father, was the first to notice.

"I start saying, 'He's in! He's in! He's in! He's in the game!' " Rick said. "Just watching my son run onto Lambeau Field after being a fan of the team for 55 years of my life was absolutely out of this world."

"I just remember everyone screaming, 'There's Colin! There's Colin!' There was just so much pride," Kathy Algiers said. "I just sort of feel like when you make it to Lambeau Field, you've really made it. So, he's gotten there."

Kaepernick took a shotgun snap that day and zipped 17 yards. On the next play, David Akers drilled a then-record-tying 63-yard field goal, That was the extent of Kaepernick's contribution to a 30-22 victory.

Now, Kaepernick returns to Lambeau as an established Packers enemy. In a playoff game against Green Bay last season at Candlestick Park, he ran for 181 yards in a 45-31 victory. In the 2013 regular-season opener, he threw for 412 yards and three touchdowns in a 34-28 win in San Francisco.

Kaepernick's focus this Sunday is on producing a similar performance, so he saw no need to run a bootleg down memory lane. Yes, he was a Packers fan growing up. And, no, that doesn't matter to him now.

Asked if a playoff game at Lambeau Field was his dream scenario, Kaepernick said: "I don't think my dream was to play in freezing weather."

Then he forced a smile.

Kaepernick was born in Milwaukee on Nov. 3, 1987. His birth mother gave the baby to a young couple from Fond du Lac, Wis. -- Rick and Teresa -- who had lost two infant boys to heart disease. They welcomed Colin to a family that already included a son named Kyle and a daughter named Devon.

In 1991, the family headed west. But they'd take family vacations back to Wisconsin in the summer, careful to coordinate the days with Packers training camp. Rick was among the most enthusiastic of the bunch. When he was 10, he had his photo taken with Fuzzy Thurston, the Packers' legendary offensive lineman. His favorite player was running back Jim Taylor.

Rick, 58, is quick to assure the 49ers fan base that he is no longer a Packers fan. The Kaepernicks -- even those in Wisconsin -- converted in an instant shortly after 3 p.m. PDT on April 29, 2011, when the 49ers traded up nine spots to the fourth pick of the second round.

Now, Cherie Kaepernick, the quarterback's 84-year-old grandmother, proudly flies a 49ers flag outside her home in New London, Wis., about 40 miles from Green Bay. Kathy Algiers (Teresa's sister) planned on wearing her 49ers jersey to work Friday as the business office manager at the Fox Valley Pulmonary Medicine center in Neenah, Wis.

They'll be there Sunday, adding another icicle to the family tree.

"There's so much history at Lambeau that when Colin played there last year it was really, really exciting," Kathy said. "Now, he's going to be starting. My biggest emotion would have to be pride."

Follow Daniel Brown at Twitter.com/mercbrownie.