A Perth man who was accused of molesting two children he looked after over the course of two years has been cleared of all charges.

Jacob Bowen, 25, appeared in the WA District Court on Tuesday for the 12-person jury to deliver their verdict on nine sexual assault charges made against him by the young pair of siblings.

Jacob Bowen. Facebook

In closing statements, defense lawyer Elizabeth Needham argued Mr Bowen had a good relationship with both of the children prior to their allegations being made and because, in part, the dates of the offending could not be confirmed, it appeared they had “made up” their stories.

“Mr Bowen doesn’t know why these allegations have been made, nor does he have to prove why they have been made,” she said.

Ms Needham said some of the acts described by the children were implausible and it was likely a family breakdown in 2017 had played into their want for attention.

She said, in particular, the nine-year-old girl often made new admissions to her mother, which in turn resulted in four police interviews.

Ms Needham said her demeanour in the recorded evidence was “telling”.

“Look at her as the story grows,” she said.

“This isn’t a child who has been dreadfully embarrassed by her first disclosure. [These are] fresh allegations that are almost gymnastic in their quality.

“This is creating a story. She likes writing. I suggest to you here she was writing a story.”

Ms Needham said the girl's 12-year-old brother had once confided to a police officer his sister’s allegations were having a serious impact on the family.

That argument suggests that if someone doesn’t complain at the first opportunity ... he must be lying. They must be a liar. Crown prosecutor Kade Rosenthal

She said once Mr Bowen heard the allegations made against him, he immediately went to police in order to give an interview.

However Crown prosecutor Kade Rosenthal argued both children were consistent in their accounts, and there had been opportunity for Mr Bowen to commit the offences as he was charged.

Mr Rosenthal said it was highly unlikely the children had made up their allegations and pointed to several moments in a police interview when the young girl had "burst into tears and had to have a break".

"Did you get the impression this is a nine-year-old child putting on a show ... manufacturing tears?” he said.

"If [she] was making up these allegations you wouldn’t expect those emotions from her."

Mr Rosenthal said the jury should be mindful of the children’s ages when they spoke to their parents and authority about what happened, and it was dangerous to consider how long there had been between the alleged incident and their disclosures.

"That argument suggests that if someone doesn’t complain at the first opportunity ... he must be lying. They must be a liar," he said.

Mr Bowen held a tissue and wiped his eyes while Mr Rosenthal delivered his final address, and his family members excused themselves from the courtroom.

Following directions from Judge Ron Birmingham, it took the jury just more than three hours to return a verdict of not guilty on all charges.

Mr Bowen’s family cried and hugged him outside the courtroom after the acquittal, and he thanked them for their ongoing support.