Frank Houston was "not lucid, he was not in a good space" only weeks before his death in November, 2004, his son and Hillsong Church founder Brian Houston said during an interview on Thursday, after Maitland Christian Church pastor Bob Cotton alleged Assemblies of God pastors were kept in the dark about Frank Houston's child sex offending.

Brian Houston told 2GB's Ben Fordham it was "very silly" of churches to "knowingly" invite his father to preach by 2004 "because he had significant dementia by then". The interview came after weeks of questions to Prime Minister Scott Morrison over whether he sought to have Brian Houston invited to a White House State dinner with President Donald Trump in September.

Frank Houston preached at Maitland once, "prayed over" people at a Central Coast congregation in the period before his death and was prominent at a Windsor evangelical church congregation, immediately after the Assemblies of God substantiated allegations in 1999 and 2000 that he sexually abused an Australian boy and up to six boys in New Zealand.

Frank Houston's credentials were removed but he was allowed to tender a resignation letter and retire on a church pension after a meeting of "special elders", including Brian Houston, at Hillsong Church on November 29, 2000.

Minutes of the meeting, tendered to the child abuse royal commission, show the "special elders" discussed "the apparent moral failure by Frank Houston some 30 years ago", and agreed Frank Houston would be thanked "for his immeasurable contribution to the church".

In his resignation letter Frank Houston thanked "the eldership" and said it had been "a privilege to minister in the church and to work with you all". There was no mention of any reason for his "retirement".

On Thursday, in response to questions about an October 18 Newcastle Herald article detailing a recording of Frank Houston's one-hour sermon at Maitland in September, 2004, Brian Houston said his father had dementia by then "to such a degree he hardly knew who he was".

"So I'm glad I wasn't there listening to an hour of his sermon because by then he was fully, virtually incoherent," Mr Houston said of the Maitland preaching.

"I can tell you he could have said anything by then because he was not in a good state. He was full of dementia."

Mr Cotton stood by his claim that he and other Assemblies of God churches where Frank Houston preached or prayed over people after 1999 and 2000 were not aware of substantiated serious child sex allegations involving multiple children.

He has previously said he supported Frank Houston until his death and allowed him to deliver a sermon because he believed the "serious moral failure" referred to in a "highly confidential" letter on December 24, 2001, restricted to pastors, related to a sexual relationship by Frank Houston, a married man.

While there was some knowledge of an incident in New Zealand in the 1970s where Frank was alleged to have "patted a teenager on the bum", it was presented as a relatively minor incident in a church where "the laying on of hands" by pastors was expected when they prayed for people.

Mr Cotton declined to comment on Brian Houston's allegation on Thursday that Mr Cotton "knew 100 per cent that my father had been accused of abusing boys, or at least one boy at that time", because of an ongoing NSW Police investigation into Brian Houston and Assemblies of God's handling of the allegations. The Assemblies of God became Australian Christian Churches in 2007.

Mr Cotton said documents presented to the royal commission and material already in the public realm supported his statements.

Mr Houston on Thursday said he was unaware of the 2004 Maitland recording until the Herald article was raised with him. Mr Houston has previously said his father "never, ever preached again anywhere after I confronted him in my office in mid to late November, 1999".

In the recording Frank Houston talks about his wife Hazel's death in a Central Coast McDonald's restaurant months earlier, but speaks clearly to the Maitland church congregation about faith and the need for people in the church to understand they are important to God.

He asks rhetorically if "baptism with the holy spirit" is "only for certain people like pastors and leaders of churches and leaders of home fellowship groups" or "does he want to fill you and everybody else with his holy spirit?"

"God has no favourites. You are important to God," Frank Houston said before inviting the congregation to repeat "I am important to God".

"Do you make God important to you and believe him? Trust his word? He won't fail you. He said he wouldn't fail you," Frank Houston is recorded saying.

He told members of the Maitland congregation "You are a Christian this morning because you believed God. So just have faith in God."

He can also be heard talking directly to a "good-looking" boy with curly hair and other children and teens in the church.

"This curly-headed young man... what a fetching young fellow he is. Curly hair, sort of. Good looking. It's not your fault you're good looking. Thank God you are. Who wants to be ugly when you can be good looking?" Frank Houston is recorded saying.

On Thursday Brian Houston said the recording and its contents were "news to me" but his father was "specifically told not to preach again and so I'll say it again, he by then was very, very given over to dementia".

In his statement to the Royal Commission into Institutional Responses to Child Sexual Abuse in September, 2014 Brian Houston said he was "aware that Frank was in the early stages of dementia" in late 1999 when the first child sex allegation was raised with him.

"I am also aware that his memory deteriorated very quickly because of dementia after 2000," Brian Houston said in his statement.

The royal commission found Brian Houston had a conflict of interest in his handling of allegations about his father, and was the sole conduit of information from Frank Houston and the first victim, Swansea man Brett Sengstock, to the Assemblies of God national executive at crucial points as the executive considered how to respond.

The royal commission also found the allegations were not reported to police or the Commission for Children and Young People, despite the commission in August, 2001 reminding the Assemblies of God of the importance of reporting completed investigations from the previous five years. The call would have included the Frank Houston allegations.

Brian Houston on Thursday repeated his evidence to the royal commission that Mr Sengstock did not want the matter raised with police and it was his "prerogative to make a report to the police if he wished" because he was an adult, aged 36, by 1999.

Former Assemblies of God national secretary Keith Ainge told the royal commission in a statement that the church leadership "did consider whether we needed to compulsorily report the offence to police".

"However, my recollection is that legal advice had been obtained and this advice was to the effect that the complainant could report the matter to police given his age, and that there was no obligation on the national executive to report the matter to police," Mr Ainge told the royal commission.

"I do not recall where the legal advice came from or who sought the legal advice."

On Thursday Ben Fordham challenged Brian Houston about the use of the term "serious moral failure" in church documents to describe why Frank Houston stopped formal ministry.

"Why didn't people say 'Listen, he's a child abuser, he's a paedophile'?" Mr Fordham said.

Mr Houston said it was a "fair question and to be honest, I wish they did take a harder line".

"You're telling me all sorts of information I haven't heard. The reality is Frank knew he was sacked, he knew he wasn't to preach again," Mr Houston said.

"The question is whether other people knew," Mr Fordham said.

Mr Houston replied: "Whether they did or not it certainly wasn't my fault."

Hillsong Church and Brian Houston were contacted for comment.