Traveling with small children is hard for any parent, especially when their child is sick.

Traveling is particularly hard for Kelsey Zwick, whose twin daughters Lucy and Eva were born premature at just 29 weeks. Lucy suffers from a chronic lung disease called Twin Transfusion Syndrome, which means that Kelsey needs to travel with a portable oxygen machine at all times.

A man recently saw Kelsey boarding an American Airlines flight and sit in her coach seat with Lucy and the oxygen machine. As she boarded, Kelsey had to walk past the spacious and luxurious first class section.

Kelsey and Lucy were traveling to see “her ‘friends’ at” the Children’s Hospital of Philadelphia. Kelly boarded the plane first, and she tried to joke with her fellow travelers about passengers being forced to sit near her “yelling-but-happy baby.” Suddenly, a flight attendant approached Kelsey and told her something that she was not expecting to hear: a passenger who wished to remain anonymous had offered his first class seat to Kelsey and Lucy!

“Not able to hold back tears, I cried my way up the aisle while my daughter Lucy laughed!” Kelsey recounted on social media. “She felt it in her bones too… real, pure, goodness. I smiled and thanked you as we switched but didn’t get to thank you properly.”

This meant that Kelsey and Lucy were able to stretch out and relax in first class! Kelsey added that she can’t wait to tell Lucy about this “random act of kindness” when she’s old enough to understand what happened.

Kelsey concluded her post by pledging to pay this act of kindness forward in the future! Her post has since gone viral, touching the hearts of people all over the world who will hopefully pay it forward as well.