The pair disappeared after they left Kawhia Harbour in Waikato on a small catamaran more than three weeks ago.
Que’s mother, Ariane Wyler, believe they were on their way to Australia – or were there already.
New Zealand police called off their search for the pair on Tuesday, but said it remained a missing persons inquiry.
Ms Wyler earlier implored Australian authorities to pick up the search, saying she believed they would not be far off the Australian coast. She has hired a Child Recovery Services contractor to find them.
Police said Interpol was involved and had been in contact with the Australian authorities.
However, without evidence of what direction Mr Langdon sailed in, Australia was one of many possible destinations.
Police remained hopeful Mr Langdon would make contact with a friend or family member.
Australian Federal Police refused to comment on whether they would take any action.
“You need to talk to New Zealand police, it’s a matter for them,” a spokeswoman said. (radionz.co.nz) [/restrict]