A mother in Ottawa says her child arrived from an Air Canada trip as an unaccompanied minor this month with someone else's passport.

Erin Hartree-Novak of Ottawa told Daily Hive that her 11-year-old was in Mexico with their grandparents for spring break but had to come home unexpectedly.

Hartree-Novak was grateful to find a direct flight into Montreal and paid about $100 for Air Canada's unaccompanied minor program. The child's grandparents dropped them off at the Puerto Vallarta airport with their documents, which were placed in a pouch with their name.

Hartree-Novak picked her child up in Montreal and was handed the pouch with her youngest's name on it.

But on Thursday, when she got around to emptying the pouch and putting things away, she realized the passport in the bag was someone else's.

"I was almost 100 per cent sure there had been a mix-up at the airport," she said. "I have no way of getting in touch with this family. It's another child's passport."

Hartree-Novak’s child arrived with their own unaccompanied minor documents and boarding pass, but when they opened the passport, they realized it was someone else's. (Submitted)

There was another unaccompanied minor flying with Hartree-Novak's child, and the family wonders if their passports got swapped.

She called Air Canada right away but said the first agent was unhelpful and didn’t appear to know what to do. When she called back a second time, she got a more receptive agent and was told the airline was reaching out to the other family to see if they had the missing passport.

Thursday was filled with questions for Hartree-Novak as she Googled rules about possessing someone else's passport. She didn't want to contact the federal government right away because she was worried it might get both children's passports cancelled and spark a lengthy re-application process.

She's giving Air Canada 24 hours to figure out the situation before she reports her child's passport lost. She's prepared to go to the Ottawa airport to give back the other family's passport and facilitate a swap.

Air Canada has not responded to a request for comment on the situation at the time of publication.

Air passenger rights advocate Gábor Lukács encouraged Hartree-Novak to hold Air Canada responsible for any expenses incurred during the process of getting the passports back to their rightful owners.

"Wow, major screwup by the airline," he said.

Hatree-Novak is disappointed with how Air Canada handled her complaint at first, calling the first agent’s helpfulness "shockingly poor."

"From what I could tell, the only thing they could tell me to do was to go to their website. And it"s difficult for me as a native English speaker; I can only imagine if someone who had just flown in from another country was told the same thing."

Hartree-Novak has lodged a formal complaint about what happened.