The championships, hosted by the Amateur Muay Thai Association of Thailand, are considered the Olympics of the sport, being the highest level of competition for amateur youth athletes from around the world.
Their dad and former kickboxer, Bevan Taylor, said despite a big fundraising effort over the past few months, they had only raised about $5000 - enough for a ticket for just one of the siblings.
"Kawhia's sort of off the beaten track. We hardly even have a gym," he said. "So that's our challenge. We were hoping to get the three over and myself, their dad and trainer."
Taylor said they had applied for sponsorship from various community groups. One suggested it would be able to donate a significant chunk of what was needed but was later unable to give as much.
"We tried to ring a few other places, but they've said it's too late to make applications. So it's a little bit disappointing."
Just last month, they had their first trip out of Kawhia; spending a month in Auckland training for the competition. Among their trainers was former heavyweight boxer David Tua, who gave them free sparring sessions every day.
At this stage, only Tokomaru will travel with the team, and brother Tainui and sister Aotea will cheer him on from home.
Taylor said he now was making a last-ditch effort to try to get all three of his children to the competition.
"They deserve this sort of opportunity.
'I just believe they've got the talent and the power to do this."
The teens, who are named after the waka that brought their ancestors to New Zealand, have always had a passion for sports and had a unique love of the outdoors, ever since they were toddlers.
"I wasn't used to being inside, so I bought a little pony and chucked two on the pony and one on my back and walked about 10km every day," their dad said.
As they grew older, they began to develop an interest in Muay Thai kickboxing and began fighting seasoned young fighters last year.
If they manage to get to Thailand, it will be their first trip out of New Zealand.
To donate, visit: givealittle.co.nz/cause/thailandgoldcup