​Kaitlyn Hayes has a little brother who loves getting mail and collecting stamps, so she's gathering some as a surprise for his upcoming birthday — and she needs your help.

The 12-year-old girl, who lives in Nova Scotia, has started a campaign to get people to send mail to her brother, Kristian, who has autism. She wants to give him the correspondence on Sept. 2 — his 11th birthday.

Heidi Hayes, Kaitlyn's mom, says she's in awe of her daughter, who started the campaign on Facebook on Tuesday. As of Friday afternoon, her post had been shared more than 4,100 times and featured comments from people in Canada, the U.S., New Zealand, Australia and the U.K.

"Kaitlyn is so happy to be giving," said Hayes.

"When she saw that this was moving and it was actually getting somewhere, her excitement is building. She is so excited. She has her little notebook now that every day, her and her grandfather go get the mail. She's keeping a tally."

Hayes, a bank teller and single mother, said Kaitlyn is hiding all the mail for a big birthday reveal. They've received 12 letters so far.

"Honest to God, the buildup and the excitement for her is second to none," she said.

'She's his No. 1 support'

Kristian's love of mail and stamps, Hayes said, started when he was five. People on the autism spectrum can become fixated on something they love or feel passionate about, she said.

"We laugh about it because it's every day. 'Did I get mail today? Did I get mail today?'" she said.

"He absolutely adores his stamps. Nobody is allowed to touch them."

Kaitlyn's maturity and willingness to look after the well-being of her little brother is something Hayes says she still can't get over.

"She's his No. 1 support. He loves her and she loves him," she said.

Hayes said she's impressed by the Facebook post's global reach.

"There are so many kind people out there, is all I can say. It just amazes me, the kind comments and the replies. This is the time where you feel the support," she said.

The image that was shared on Facebook, featuring Kaitlyn's request to surprise her brother on his birthday. (Heidi Hayes/Facebook)

If you want to send mail to Kristian Hayes, the address is: P.O. Box 286, Stellarton, Nova Scotia, B0K 1S0, Canada