Transcript for Brotherly Love Goes Viral, Big Time Rush Surprises Bullied Sister

A story we've been waiting to share with you today. A brother's letter to santa claus. An early one, at that. It went understandably viral. 8-year-old ryan, writing that the only thing he wanted more than any other toy for christmas, was for kids at school to stop bullying his twin sister, amber. Take a look. 8-year-olds ryan and amber suffern are you typical twin siblings. But as ever, clearly attuned to the other's needs. And in the worst of time, feeling each other's pain. Something their mother, karen, discovered recently. A single mom with a part-time job, struggling to pay the family's bills. She asked her kids to write a note to santa early. I need you to go ahead and write what you want for christmas. Reporter: Ryan wrote his letter to santa almost immediately. I decided, let me take a peek. Reporter: And what he wrote, was as beautiful as it was gut-wrenching. Would you do me a favor? Read your letter out loud. Dear, santa. I wanted a remote-control car and helicopter. But I don't want that anymore. Kids at school are still picking on amber. And it's not fair because she doesn't do anything to them. And it makes me mad. I pray that they will stop. But god is busy. And he needs your help. Is it against the rules to give gifts early? Reporter: And ryan, so genuine, so pure, didn't stop there. He also asked for his sister to be able to meet her favorite band. Can you ask big time rush to come to amber's birthday party? It will make her so happy. If you can't get them to come, just get her everything she asks for. Thanks, santa. So, needless to say, i started crying. Reporter: Prior to the letter, you were aware that your daughter was suffering. She would tell me things that kids would say at school. They would call her names. Amber suffers from a few mental disorders. They would egg her on to do different things. And it was a pattern. Reporter: A pattern that karen also bullied and suicidal as a child, decided must end after her recent talk with amber. They were like, yeah. They pick on me sometimes. I feel like I want to die so they'll leave me alone. And as soon as the words came out of her mouth, I felt my heart stop. Sorry. Reporter: It's okay. I told her, I was going to do everything to protect her. Reporter: And so would her twin brother. What's it like having ryan as a brother? He protects me. Reporter: Are kids mean to you? Yeah. But I don't know why. They, like, say I'm fat, I'm stupid, I'm ugly and I'm heinous. I don't believe them. Reporter: Do you wish people would mess with you instead of amber? Yes. You don't have to do that. Reporter: Amber, did you like hearing this letter? Yes. Reporter: Did you give him a hug? Yes. Reporter: Amber, can I tell you one other thing? It's going to get better. Yay. Reporter: I promise. But what amber and ryan and their mother don't know, is that santa may have already answered her brother's letter and sent amber's favorite band, big time rush, to meet her. ♪ I decided I could give it a try ♪ Reporter: You asked can santa give a gift early? Her birthday. Reporter: Yeah. For the birthday. Hmm. I think -- I think somebody up north might have gotten this already. Let's see. I do think that -- I think somebody actually did get this letter early. Guys? Hi. Hey. Hello. How are you doing? What's up? How are you doing? Can I get a hug here? How are you? All right. Awesome. Oh, my gosh. Reporter: Amber didn't just get to meet big time rush. ♪ Worldwide ♪ Reporter: An early christmas for a deserving young girl, who already has the best gift of them all. Always love and protect her. How was that? All right? Reporter: One more. ♪ Just one thing that I know ♪ oh. You know -- that's enough. Oh. That's so adorable. I want to thank the suffern family, for joining us today. Okay. Okay. I want to thank big time rush, who came out. They're going to be -- the family's going to be their v.I.P. Guests this weekend at a big concert. I want to say to you, I said it all morning long, bullying is a scourge that is taking our most precious resource, young children in this country. We need to stop it. And so, thank you, guys. Thank you, guys.

This transcript has been automatically generated and may not be 100% accurate.