The man, who cannot be named for legal reasons, is facing trial in the ACT Supreme Court charged with 16 offences against young people, including sexual assault, indecent assault and acts of indecency.

The offences dated back to the 1970s and 1980s.

Two of the four alleged victims were the 74-year-old's daughters, while the other two were girls who had been dropped at the day care run by his wife at home, the court heard on Monday.

He pleaded guilty to three charges on the indictment, relating to touching his daughter while she was pretending to be asleep.

He has pleaded not guilty to charges relating to other acts against two of his daughters, including one incident in which he kissed a daughter, and other incidents involving two young girls dropped at the day care.

Prosecutor Trent Hickey said there was a cut-out area in the workshop space under the house, with a mattress and a sheet separating it from the main space.

Several counts on the indictment related to a young girl the man was accused of taking behind the sheet, and another count related to an incident in the back of his truck where there was a sleeping cabin, Mr Hickey said.

Mr Hickey said the jury would hear evidence that when a mother confronted the man about him speaking about sex to one of the young girls, she was told they had every right to explain the facts of life.

The mother removed her children from the family day care, he said.

The man's defence barrister, Amanda Tonkin, said he would take the stand to give evidence during his trial.

She told the court he would say that after the misconduct against his daughter – the three counts to which he had pleaded guilty – things changed and from that point he did nothing wrong.

The trial continues.