A former Families SA carer who sexually abused two young girls in his care has been sentenced to 12 years in prison - but a judge says his actions will stay with his victims for the rest of their lives.

Aaron Sean Jaede, 34, appeared by video-link in the South Australian District Court on Friday, after earlier pleading guilty to five counts of unlawful sexual intercourse with a person under 14 years and one count of aggravated indecent assault.

Jaede sexually abused the girls, who were 11 and 12 at the time, between 2014 and 2016.

Chief Judge Michael Evans sentenced him to 12 years and 18 days in prison, with a non-parole period of nine years, seven months and 21 days.

Judge Evans said Jaede took advantage of his position and abused the trust of the children in his care.

"Your actions have fundamentally altered the childhood of two young girls, to their detriment," he said.

"The memories of your actions are something that your victims will now have to live with for the rest of their lives.

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

Jaede had initially denied the offending and claimed he had been unfairly targeted because of his gender, but pleaded guilty 11 days before his trial was due to start.

Outside court on Friday, the mother of one of the victims said she was "so, so angry" at the sentence, which she believed to be inadequate.

"They took her vulnerability, they took her youth, they took her from me because she now just wants to closet herself in and try to mend," she told reporters.

"Nine years goes by in a flash."