The UN has said that the Vatican should "immediately remove" all clergy who are known or suspected child abusers.
The UN watchdog for children's rights denounced the Holy See for adopting policies which allowed priests to sexually abuse thousands of children.
In a report, it also criticised Vatican attitudes towards homosexuality, contraception and abortion.
The Vatican responded by saying it would examine the report - but also accused its authors of interference.
A group representing the victims of abuse by priests in the US welcomed the report.
In its findings, the UN Committee on the Rights of the Child (CRC) said the Holy See should open its files on members of the clergy who had "concealed their crimes" so that they could be held accountable by the authorities.
It said it was gravely concerned that the Holy See had not acknowledged the extent of the crimes committed, and expressed its "deepest concern about child sexual abuse committed by members of the Catholic churches who operate under the authority of the Holy See, with clerics having been involved in the sexual abuse of tens of thousands of children worldwide".
It also lambasted the "practice of offenders' mobility", referring to the transfer of child abusers from parish to parish within countries, and sometimes abroad.
The committee said this practice placed "children in many countries at high risk of sexual abuse, as dozens of child sexual offenders are reported to be still in contact with children".
The UN report called on a Vatican commission created by Pope Francis in December to investigate all cases of child sexual abuse "as well as the conduct of the Catholic hierarchy in dealing with them".
Ireland's Magdalene laundries scandal was singled out by the report as an example of how the Vatican had failed to provide justice despite "slavery-like" conditions, including degrading treatment, violence and sexual abuse.
The laundries were Catholic-run workhouses where some 10,000 women and girls were required to do unpaid manual labour between 1922 and 1996.
The report's findings come after Vatican officials were questioned in public last month in Geneva about why they would not release data and what they were doing to prevent future abuse.
The Vatican has denied any official cover-up. However, in December it refused a UN request for data on abuse on the grounds that it only released such information if requested to do so by another country as part of legal proceedings.
In January, the Vatican confirmed that almost 400 priests had been defrocked in a two-year period by the former Pope Benedict XVI over claims of child abuse.
The UN committee's recommendations are non-binding and there is no enforcement mechanism.
The BBC's David Willey in Rome says the Vatican has set up new guidelines to protect children from predatory priests.
But, he adds, bishops in many parts of the world have tended to concentrate on protecting and defending the reputation of priests rather than listening to the complaints of victims of paedophile priests.
Meanwhile several Catholic dioceses in the US have been forced into bankruptcy after paying out huge sums in compensation to victims of abuse by clergy.
The Vatican said in a statement following the report's publication: "The Holy See takes note of the concluding observations...which will be submitted to a thorough study and examination... according to international law and practice."
But it added that it "regrets to see in some points of the concluding observations an attempt to interfere with Catholic Church teaching on the dignity of human person and in the exercise of religious freedom" and "reiterates its commitment to defending and protecting the rights of the child... according to the moral and religious values offered by Catholic doctrine".
Archbishop Silvano Tomasi, head of the Holy See's delegation to the United Nations in Geneva, told Vatican Radio the report had failed to take into account the fact that the Vatican had made "a series of changes for the protection of children", and its efforts at reform were "fact, evidence, which cannot be distorted".
He added that the UN could not ask the Church to change its "non-negotiable" moral teachings.
Victims groups welcomed the report as a wake-up call to secular law enforcement officials to investigate and prosecute Church officials who were still protecting "predator priests".
Barbara Blaine, president of a group representing US victims of abuse by priests - Survivors Network of those Abused by Priests (Snap) - told the BBC that the UN report "reaffirms everything we've been saying. It shows that the Vatican has put the reputation of Church officials above protection of children".
"Church officials knew about it and they refused to stop it. Nothing has changed. Despite all the rhetoric from Pope Francis and Vatican officials, they refuse to take action that will make this stop."