Attorney-General Mark Speakman said the families had been through a "heartbreaking" ordeal during the last 30 years, but added it was unlikely they would receive a reply any time soon.

"I can only apologise that we haven't had a response by now," Mr Speakman told a budget estimates hearing on Wednesday.

"To be honest with you, I don't expect a response within weeks.

"It's not just me as the attorney-general, deciding to respond - there are implications for other parts of government.

"Unfortunately, a whole-of-government response has taken a very long time."

The three children went missing from the small town in the hills south of Coffs Harbour on the mid-north coast over a five-month period from 1990 to 1991.

Last month, NSW Police tripled a reward for information into the murders of Evelyn Greenup, 4, Clinton-Speedy Duroux, 16, and Colleen Walker-Craig, 16.

A $1 million reward was announced in February 2020.

The Communities and Justice Department had initially responded to the family about a year ago, but this was withdrawn after it was found to be a draft letter sent in error, Greens MP David Shoebridge told budget estimates.

"How long is a reasonable amount of time for the families to wait for a response?" Mr Shoebridge asked.

The attorney-general responded he could not give a precise answer, adding the families had been "very patient in very extraordinary circumstances".

He could not explain the delay except to say it was not "just a matter of me making an executive decision as attorney-general".

"We have to explore the onboarding of other parts of government before something can be done."

He said he would try and provide the family with an update in the coming weeks but could "not put a timeframe on a substantive response".

Australian Associated Press