The Vatican is being grilled publicly for the first time over its record of sexual-abuse cases against children and the alleged cover-ups protecting paedophile priests.
Officials will face a barrage of hard questions before a panel in Geneva such as why would they not release full data and what were they doing to prevent future abuse.
Archbishop Silvano Tomasi said such crimes could "never be justified" and every child should be "inviolable".
A fellow official said "things need to be done differently".
The Vatican earlier refused a request from the UN's Committee on the Rights of the Child (CRC) for data on abuse, and was accused of responding inadequately to abuse allegations.
Victims say they hope the hearing, which is being broadcast live, will prompt the Church to end its "secrecy".
Pope Francis announced last month that a Vatican commission would be set up to fight sexual abuse of children in the Church.
The Holy See is a signatory to the UN Convention on the Rights of the Child, a legally binding instrument which commits it to protecting and nurturing the most vulnerable in society.Suggest a correction