To protect the victims, RTÉdid not name them or their abuser.
In an RTÉ Investigates on Prime Time, some of the women at the centre of the court case come forward to tell their stories publicly for the first time - writes rte.ie
In doing so, the womenwaived their right to anonymity to name their abuser as 29-year-old Keith Burke of Addergoolemore, Dunmore, Co Galway.
In recent weeks, Burke was sentenced to seven-and-a-half years in prison, with a year suspended, after he was found guilty of raping the then three foster children between 2003 and 2007.
All three girls were under ten years of age at the time.
In a statement the HSE said that while no apology can undo the harm inflicted on the three girls, it is important that the HSE expresses a heartfelt apology at this time.
All of the relevant historic files are with Tusla since 2014.
The HSE has been in contact with Tusla in order to discuss how best to determine whether the case raises any concerns for HSE-delivered services today.
Warning: Readers may find some of the following details upsetting
One of those abused was Rachel Barry. In 2005, the then eight-year-oldwas sent to the home of Kathleen and Gerry Burke of Dunmore, Co Galway, for monthly respite care.
There she met a long-term foster child who has asked to be identified as 'Amy'. Both Rachel and 'Amy' were raped by Keith Burke.
Speaking to RTÉ Rachel said: "Myself and 'Amy' in turns had to strip down with nothing only our socks on and while he had obviously done it to 'Amy' before, he called her over and I had to watch what was happening to her."
In May 2007, Rachel told her biological mother she had been sexually abused by Keith Burke and a subsequent HSE investigation assessed Rachel's disclosure as "credible".
Rachel also reported that 'Amy' - who at that stage had been living with the Burkes for over a decade - had been raped by Keith Burke. However, at the time 'Amy' did not disclose any abuse.
Gardaí sent a file to the DPP but no prosecution followed. 'Amy' and another foster child, a boy, continued to live with the Burke family.
Four years later, in October 2011, 'Amy' came forward and told a teacher she too had been raped by Keith Burke.
Her disclosure prompted a new garda investigation, which uncovered a third victim.
'Sarah', which is not her real name, was also placed into foster care with Kathleen and Gerry Burke in 2000, aged five. She too was regularly raped by Keith Burke. 'Sarah' also witnessed 'Amy' being repeatedly raped.
Speaking to RTÉ, 'Sarah' said: "It was horrible and she was so small and she was so young. She was only a little girl and we both clicked and we both loved each other.
"I always wanted to protect her, but I couldn't. He was a beast.I was just too frightened of him."
'Sarah' left the Burke foster home in 2003but 'Amy' continued to live there until she disclosed her abuse in 2011.
At that stage, the gardaí resumed their investigations into Keith Burke, leading the DPP to press charges on more than 70 counts of sexual abuse. But Keith Burke pleaded not guilty when the case went to trial, meaning 'Amy', 'Sarah' and Rachel were forced to take the stand and give evidence.
Last July, Keith Burke was convicted following a nine-day trial, he was found guilty on 23 sample charges, including rape, sexual assault and buggery.
Just a fortnight ago, at his sentence hearing, Keith Burke finally admitted his guilt.
He was sentenced to seven-and-a-half years for the rape charges and concurrent terms of six-and-a half years and five years for the remaining charges. The final year was suspended.