A former South Australian child protection worker who sexually abused two young girls will spend at least nine years in prison.

But the mother of one of his victims said the penalty was nowhere near harsh enough for the "sicko" who took her daughter's "vulnerability".

Aaron Sean Jaede, 34, initially denied the offending — dating back to 2014 — and claimed he had been unfairly targeted because of his gender.

But he later pleaded guilty to five counts of unlawful sexual intercourse with a child under the age of 14, and one aggravated count of indecent assault.

In sentencing submissions last month, one of Jaede's victims said her life had been changed forever.

The girl said she was "extremely mad" at the State Government for failing to keep her safe.

"Sometimes I cry myself to sleep thinking about it," she said in a victim impact statement read to the court.

"I know those memories will never really go away, no matter how much I wish they would."

Jaede's defence lawyer Edward Stratton-Smith previously told the District Court his client was "deeply ashamed" of his offending and knew he had caused "a great deal of pain for the victims".

Mr Stratton-Smith said his client had been "good with children" and had not entered the profession "with a view to offend".

The District Court heard Jaede raped one of his victim's five times over the course of eight months, and indecently assaulted his second victim several months later.

In handing down the sentence today, Chief Judge Michael Evans said the offending was the type that caused "outrage and revulsion in the community".

Judge Evans told Jaede he had "taken advantage" of his young victims, who were aged between 11 and 13 at the time of the offending.

"General and personal deterrence are key [for this kind of offending]," he said.

"Your actions have fundamentally altered the childhoods ... of your victims.

"They were supposed to be protected from ... the likes of you."

Judge Evans imposed a sentence of 12 years in prison, with a non-parole period of nine years and seven months.

Family outraged by 'inadequate' sentence

Outside court, the mother of one of Jaede's victims said she was outraged by the length of the sentence.

"I'm so angry. So, so angry," she said.

"Nine years is not an adequate sentence for the rape of a minor.

"[He] took her vulnerability and her youth... what kind of sicko does that?

"He's going to be 45 and out free.

"Nine years goes by in a flash and he's already working on his business courses [in prison]."