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/ Source: TODAY
By Allison Slater Tate

Stories about babies on airplanes do not always end with parents crying happy tears, but as Florida mom Kelsey Zwick found out, sometimes the skies are unexpectedly friendly.

When Zwick and her 11-month-old daughter, Lucy, boarded American Airlines Flight 588 from Orlando to Philadelphia last week, the mom from Melbourne, Florida, was already thankful to be on the flight at all, she told NBC News. The two were heading to the Children's Hospital of Philadelphia (CHOP). Lucy, who was born prematurely along with her twin sister, receives treatment there for chronic lung disease.

"Not everybody gets the opportunity to get the best care for your children. I was just grateful to be on that flight," Zwick said.

After pre-boarding and settling herself and Lucy into their seat with her diaper bag and Lucy's large oxygen tank, Zwick was surprised when a flight attendant approached them and told her a passenger from first class wanted to switch seats with her.

"At first, I didn’t really understand what she was saying," said Zwick. "When I realized that it was someone showing kindness to us, I just started crying."

The good Samaritan was Jason Kunselman of Mechanicsburg, Pennsylvania, who had spotted the mom and baby as they boarded the flight. "She had gotten on the plane on the line ahead of me," he told NBC News. "Other people started piling on, and I thought she’d be more comfortable in my seat."

Kunselman said his birthday was the day after the flight, and he was grateful to have been able to help Zwick and her daughter. "It was the perfect birthday gift, seeing that I could help someone else out and make someone happy," he said.

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The seat exchange was quick but meaningful. "She walked up crying. I’m not much of a crier, but it was hard not to," Kunselman said. "One flight attendant put her hand on my cheek and said, 'God will repay you for this.'"

Though she tried to find him after the flight, Zwick missed Kunselman when they landed in Philadelphia. "I was waiting at the gate to say thank you so much, but I must have missed him," she said. That night in her hotel room, she decided to post about the encounter on Facebook.

"To the man in 2D... Thank you. Not just for the seat itself, but for noticing," she wrote. "For seeing us and realizing that maybe things are not always easy. For deciding you wanted to show a random act of kindness to US. It reminded me how much good there is in this world. I can’t wait to tell Lucy someday. In the meantime... we will pay it forward. AA 588 passenger in seat 2D, we truly feel inspired by your generosity."

By the next morning, the post had gone viral. It has currently been shared more than 461,000 times. "It was that small act of kindness that I think the world is hungry for," Zwick said. Kunselman's wife was the one who alerted him to the viral Facebook post. "Reading Kelsey’s story on Facebook, it was heartbreaking," he said. "A young mother shouldn’t have to go through that with her children. Hopefully, American Airlines will upgrade her every time."

Kunselman was referring to Lucy's rough start in life. When Zwick was 17 weeks pregnant with Lucy and her identical twin sister, Eva, she found out the babies had twin to twin transfusion syndrome, a potentially fatal condition that affects 10 to 15 percent of all identical twin pregnancies in which the embryos share a common placenta.

Identical twins Lucy and Eva Zwick, pictured here with their parents, were born at just 29 weeks gestation after suffering from twin to twin transfusion syndrome in utero.Courtesy of Kelsey Zwick and Winnie Palmer Hospital for Women and Babies

The day they found out about the condition, Zwick and her husband flew to Houston, Texas, to undergo fetal surgery to save the babies' lives. She delivered Eva and Lucy at 29 weeks gestation, and both girls weighed under 3 pounds each.

Lucy came out blue and had to be intubated and placed on a ventilator for the first week of her life. Though the ventilation saved her life, it also left scarring in her lungs that caused her chronic lung disease. Zwick has been traveling to CHOP with Lucy for treatments every three months.

"You never expect this to happen," Zwick said. But I think for us, it’s really a story of faith. It stretched our faith. It gave us hope every day that God brought these children into the world, so he has big plans for them."

This will be the Zwicks' first Christmas with their daughters. "It’s been a special year for us, and it’s also been the hardest year of our life," she said. "It has made us the most grateful, present, parents. We didn’t know if we were going to get to have them. We’re just so happy."

The Zwicks are looking forward to their first Christmas together. "We’re grateful to have them," said Kelsey. "It’s been a special year for us, and it’s also been the hardest year of our life." Courtesy of Kelsey Zwick and Winnie Palmer Hospital for Women and Babies

That's why, she explained, it moved her so much when Kunselman gave her his seat. "I was so emotional because we had such a year, and someone seeing me and saying they wanted to do something kind, it touched my heart," she said.

"It wasn’t about the seat. It wasn’t about it being in first class. It was about someone showing that kindness when they saw me in that vulnerable state," she added.

Both Zwick and Kunselman said they hope that their story will encourage others to act out of kindness. "I thought nothing of it when I did it. It's been very heartwarming to see all of the messages from everyone. Hopefully this will be the season that people will pay it forward," he said.

"I hope it goes beyond the holidays, beyond December," Zwick said.

Stephan Kozub of NBC News contributed to this story.