Children's campaigners have demanded action after an investigation revealed vulnerable teenagers are being looked after by foster carers who have allegations hanging over them.
Troubled youngsters taken into care are also being placed long-term with unapproved foster parents and with care staff whose Garda vetting is out of date, it has been revealed.
The Health Information and Quality Authority (Hiqa) - the State's health watchdog - said it could not disclose the severity or nature of "upheld" complaints against carers who continue to foster children.
But the authority attacked the Health Service Executive (HSE) for its "lack of urgency" in carrying out investigations into the allegations.
Tanya Ward, chief executive of the Children's Rights Alliance, said action was needed immediately to deal with the serious concerns raised by the watchdog report.
"Children in the care system are among the most vulnerable children in the State, and many have past experiences of abuse and neglect," she said.
"These children have a clear right to be provided with special protection and assistance. Over many years, successive reports have shown how we have utterly failed children in care... Hiqa has once again revealed gaping holes in this still struggling system."
There are 6,400 children in State care in Ireland with around nine in 10 in foster homes.
Gordon Jeyes, national director at the HSE, said it was already carrying out reforms ahead of the setting up of the Child and Family Agency. He said: "The picture is an improving one.
"As a society we can be proud of our family-based approach to providing care for children. The proportion in care in Ireland looked after in foster care is far higher than in comparable countries."