When eight-year-old Ryan wrote an early Christmas list for Santa, he only wanted two things. The first, for the kids at his school to stop picking on his twin sister, Amber. The second, for Amber's favorite band, Big Time Rush, to come to her birthday party to make her happy.

The heartbreaking note he wrote on behalf of his sister, shared on Facebook by their mother, was picked up by CNN earlier this week, and it ended up reaching the eyes of the boy band.

Big Time Rush were in New York this week for Nickelodeon's WorldWide Day of Play. With the help of Good Morning America, they flew Ryan and Amber in from North Carolina to join them. It was the first time the kids had ever been in an airport. The family was also given VIP passes to their concert.

The guys of BTR -- Kendall Schmidt, Logan Henderson, James Maslow and Carlos Pena -- stopped by HuffPost Live on Thursday and talked about what it was like to meet the young siblings.

"Ryan is so exceptional. He literally wrote that he didn't want anything -- no cars, no nothing -- just please, help my sister out," Pena said. "For an eight-year-old to be like that? To me, that's so inspiring."

Henderson also noted that, even after they met him in person, Ryan still didn't want the cameras on him.

"What a cool kid," he said.

Watch the video above to hear more about Ryan and Amber's big GMA surprise.