A source tells PEOPLE that Brady, 45, visited New York City and "cheered on Jack" as the 15-year-old's team was winning on Monday afternoon.
"He and a friend kept to themselves," the source says. "His other kids weren't with him this time. he seemed smiley and would yell out to cheer on Jack."
The day before, Brady and the Buccaneers trounced the Saints 20-10 in New Orleans, but not before a brawl between the two teams during the fourth quarter led to at least one suspension. Brady was not involved in the fight but showed his frustration in the first quarter when he threw and broke a tablet on the sidelines.
Tampa Bay is now 2-0 to start the year, which is the 23rd season of Brady's career.
"Great win to get to 2-0," Brady said in a video posted to Instagram after the game. "Get ready for next week. Green Bay coming to town, let's go."
Brady also traveled to New York earlier this month to watch one of Jack's football practices, a source told PEOPLE.
"Tom was in great spirits and chatted to all the parents," they said. "He flew all the way in for the scrimmage."
Aflo/Shutterstock Tom Brady and son Jack
"He's such a sweet dad and is always there for Jack," the source added of Brady's relationship with Jack, who he co-parents with ex Bridget Moynahan.
RELATED VIDEO: Tom Brady Apologizes After Breaking Tablet Before All-Out Brawl at Bucs vs. Saints Game
Sources told PEOPLE that Brady's decision to un-retire has led to tension with Bündchen, 42, who wanted him to stay retired when he made the decision in January, only to un-retire two months later.
"There's a lot of tension. She was so happy when he announced his retirement, and she wasn't thrilled at all when he went back on that," one source said, adding that Brady "knows that this is his last season" in the league "if he wants to stay married."
Another source said Brady makes sure to find time for his family. "No other husband gets six months off a year to be totally devoted to just their family," they explained. "And during the season, yes he travels for games and trains, but he's with his family a lot too."