"I'm an outdoor, on-site painter, which requires a lot of time away from home," he told TODAY Parents. "When I realized — especially when the kids were little — that I wanted to be home with them more than out painting on the side of the road somewhere, I basically put the painting on hold and focused on my family."
But he still drew all the time on whatever happened to be around. One day, he doodled on a napkin that ended up going into Sean's lunchbox, and an idea took hold.
Flynn started drawing on Sean's lunch napkins regularly, sometimes marking the day of the week, or how many days left until summer vacation, or cheering him on when he had track meets. When Molly started school, she started receiving lunch napkin art from her dad as well. Eventually, Flynn even compiled his creations into a self-published book.
"Sean has always gotten a kick out of [the drawings], and still does," said Flynn.
The subject matter of the napkin art has changed quite a bit. Early works, when Sean was 7 or 8, incorporated his favorite video game or cartoon characters. More recent napkins show "more cerebral, esoteric things," his dad said.
It's "basically been an ongoing conversation we've been having for the last decade," Flynn said.
Sean said he didn't see the napkins as anything profound, but he did appreciate them. "I just enjoyed seeing them in my lunchbox everyday," he told TODAY Parents.
Last week, however, Flynn drew a special picture for Sean's lunch: a sketch of Sean in his graduation gown, a guitar slung on his back, as he walked away toward the sun with a diploma. The napkin marked a big milestone: Sean is graduating from high school this week.
"When I started drawing these napkins almost a decade ago, I knew I'd be drawing this napkin one day," Flynn wrote on a Facebook caption for the picture. "Well, here we are. I'm beyond proud. I'm beyond a number of emotions at the moment, but all of them as positive and good (although bittersweet as HELL) as they can be. But all of them are superseded by optimism for Sean's future and gratitude for the privilege I've had to be a part of it all."
Sean will be heading to the University of Washington in Seattle in the fall, where he plans to study pharmacy. His departure is bittersweet and emotional for Flynn and his wife, Angela.
"The last week has been an absolute roller-coaster," said Flynn. "On one hand, we have no regrets. We've left everything on the table parenting-wise, and I can't think of anything we would do differently. On the other hand, we're extremely close, and the combination of being insanely proud of him and knowing that he's about to start the next phase of his life leaves me a complete mess.
"And yes, the last napkin was extremely difficult. I'm surprised the ink didn't run."
Flynn still has three years' worth of lunch napkins to draw for Molly, and he plans to paint again more now that his children are older. He also said the lunch-napkin art for Sean might not end with high school.
"I'm absolutely going to send him napkins in college," he said. "They'll just be in care packages."