An Australian who fathered surrogate twins with a Thai woman has been charged with sexually abusing the children.

The man, who cannot be identified, has been charged with indecent dealings of a sexual nature with the children while they were under 10.

Court documents reveal he has also been charged with possessing child abuse material which was found after a raid on his home.

The man involved denies the allegations, which will come before court later this year.

The Thai surrogate mother, Siriwan Nitichad, also known as Aon, lives in the Petchabun province 400 kilometres north of Bangkok.

Encouraged by a relative and with her husband's agreement, Aon agreed to act as a surrogate for a couple from Australia who could not conceive on their own.

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"They contacted us to be a surrogate," she said.

"They asked whether we wanted to meet them first or if they should meet us first, so that they could see how I look like and we could see how they looked like, to see if it was fine for us."

Once the decision was made Aon met the couple, who had travelled to Thailand.

"They said they were just married and they really wanted to have a baby so much," she said.

"She said her husband wanted to have a baby so much, please help them, please help them.

"She held my hand and said please help them."

Aon agreed to use her own eggs.

"I thought she really could not [use her own eggs] because I saw she was quite old already," she said.

"They must be really having problems and really could not find anyone else."

Aon says she was paid a total of 170,000 Thai baht for her services - about $5,500.

She says there was mention of extra money because she had provided the eggs, while the sperm was supplied by the Australian man, but the extra payment never eventuated.

Aon gave birth to twins several years ago.

"After the birth the babies were not so strong so I was worried," she said.

"They were checked on many things, they had lung problems.

"When it was time to give them up, I actually did not want to because I was worried.

"They were about four to five months old.

"They were so lovely, I wanted them to stay with me, I did not want to let them go.

"If they asked if they could cancel their payment and we kept the babies, I would definitely have said yes."

Children suffered as marriage broke down

The Australian couple took the twins back to their home in Australia - and it was then things took a turn for the worse.

Court documents reveal the father became unemployed, allegedly had a violent temper, and the marriage broke down.

The children were having night tremors and had begun to wet the bed.

Last year the authorities charged the father with indecent dealings with the children.

Aon and her husband, Kosin Suthivarakorn, were told of the allegations in June 2013.

"I felt terrible, I felt very bad, I don't know how to describe it," Aon said.

"I knew only, when they came to talk to us they wanted to have a baby, will love them, will take the best care for them - I felt bad."

Dilemma over whether to send children back to Thailand

The children are now in the care of the ex-wife of the accused man, and Australian child welfare authorities are now working on longer-term plans for their care.

Ilya Smirnoff runs Childline Thailand, a child welfare organisation which runs safe houses for children and has been asked to help with the case.

"We have been contacted by the international social service representative from Australia to make an assessment for the possible placement of the children back to Thailand," Mr Smirnoff said.

That would reunite the children with their surrogate and biological mother, but there are complications.

"They don’t even speak any word of Thai, they don't know that they are half Thai or have any connection to Thailand," Mr Smirnoff said.

"They consider themselves to be fully Australian."

The case is likely to increase the scrutiny on Thailand's long unregulated surrogacy laws.

Fears paedophiles exploiting system to get access to children

After the case of Baby Gammy, the baby boy with Down syndrome left behind by his Australian parents, the ruling Thai military has been working to introduce new laws banning commercial surrogacy.

"A lot of people are also approaching this subject from the rights of the people who seek surrogacy, the rights of the surrogate mother, the rights of the hospitals and clinics," Mr Smirnoff said.

"But very few people, I think, until this time, were talking about the rights of the child.

"[That] they have to enjoy all their rights and protection is one of the fundamental rights they need to enjoy.

"It is a state party duty to put those checks in place, to ensure that the child is protected and all violence towards them is being prevented."

Mr Smirnoff says it is possible paedophiles are exploiting a loophole in the system.

"It's not just this system, they (paedophiles) are quite good at abusing any system. Especially this system, because right now it has these big sort of chunks that are missing, so they'll just abuse it, abuse the opportunity," he said.

"If you know you are a paedophile and you think, 'How can I get access to a child reasonably easy and reasonably soon?', surrogacy is definitely an interesting opportunity for you, especially if you have the money."