The 45-year-old man, who cannot be named, pleaded guilty to 38 offences including sexually penetrating, indecently dealing and indecently recording children.

The abuse happened between August 2012 and December 2016 when the victims were aged between five and nine, the WA District Court heard.

The man also pleaded guilty to possessing and distributing child exploitation material.

Judge Stephen Lemonis said it was an aggravating factor that the man targeted girls while they slept and took them to different parts of the house to abuse them.

"Your conduct in taking advantage of and abusing these young children is reprehensible," he said.

"These offences are not reflective of you having given way to an impulse on one occasion or occasions.

"Rather, you've chosen repeatedly to commit serious offences and created opportunities to do so."

Judge Lemonis noted two girls were awake during the abuse and they told investigators they were terrified and crying.

He commended the girls for their "remarkable courage".

Judge Lemonis said the man grossly abused the trust of the parents too, but accepted he was remorseful and apologetic.

The man must spend at least eight years behind bars before he can be eligible for parole.

Australian Associated Press