A Montreal couple unknowingly invalidated their children’s passports with a stroke of a pen, a simple mistake that added thousands to the cost of their winter getaway.

Muriel Frenois and Gilbert Delambre were looking forward to a budget-friendly trip to Cuba with their two adopted sons. But when an Air Canada employee spotted signatures written by the parents on the young boys’ passports, they were told the documents were invalid and they would not be allowed to fly.

Canada’s general passport application for children states: “Children 11 years of age or over must sign their usual signature. At no time should a person other than the child sign in the signature box in section 1, without exception.”

Frenois and Delambre said they had no idea about the rule when they filled in the boys' names.

Stranded at the gate, the airline directed them to a government hotline where they could book an appointment to apply for two emergency passports. Those cost $500. Desperate to salvage the vacation, the family of four was forced to rebook their flights.

What was supposed to be a cheap trip ended up costing nearly $8,000.

“I don’t understand how such a little mistake can lead to such serious consequences,” Frenois told CTV Montreal. “I know all about government forms. I adopted two children. So immigration stuff has no secrets for me.”

Frenois and Delambre admit the incident was their fault. Still, they say the situation was handled poorly by Air Canada.

“We felt it was unfair,” said Frenois. “They didn’t help. They didn’t give any assistance.”

The couple said their children travelled to Cuba nine months earlier on the same passports, but on a different carrier.

Air Canada told CTV Montreal it had no choice but to follow the law, regardless of previous travel on other airlines, noting failure to do so would result in fines.

Frenois and Delambre want to save others from making the same costly error, warning it’s bound to happen to more young Canadian families.

“Our situation will happen again for sure,” Delambre said.

With a report from CTV Montreal’s Denise Roberts