It was a case of one too many when a young mother and her twins set off for a family trip to Australia.

Aimee Moutray arrived at Auckland International Airport with her 18-month-old identical twins Arliyah and Janade at 5am on Monday.

The trio were flying Jetstar to the Gold Coast where the toddlers were to be flower girls at Ms Moutray's cousin's wedding next Friday.

But when they got to the check-in counter Ms Moutray was told the twins were not allowed to fly without a second adult.

Ms Moutray booked the $481 return tickets online over a month ago. She went on to the Jetstar website where it told passengers wishing to travel with more than one infant (a child under two years) to phone customer services for assistance.

With the help of a Jetstar representative, Ms Moutray placed an online booking for one adult plus an infant and an extra child seat. She was told this arrangement would cover her and the twins.

Ms Moutray said the whole situation was pretty upsetting.

She told check-in staff that the twins were capable of sitting in a seat and asked if one of the flight crew could hold one of the girls during take-off and landing or if they could ask another passenger if they would be willing, but she was told this was not possible.

Ms Moutray has been frantically trying to arrange another flight, but needs the refund before she can re-book on another airline - she has been told it could take several weeks for the money to come through.

Her mother Angela spoke to a manager at Jetstar and asked if the company would give Ms Moutray a seat for a second adult so the family could make it to the wedding, but was told the only option was a refund.

Simon Westaway, corporate relations, did not know how the phone booking was able to go through, but said a refund should be with the family in the next couple of days.

"The issue is, basically, because they are both under 2 ... they can't hold a seat in their own right," he said.

Under-2s must be accompanied by an adult over 15 years old and are required to sit on an adult's knee during takeoff and landing.