The head of Save the Children Australia says there needs to be far greater transparency and oversight of Australia's offshore detention centres on Papua New Guinea and Nauru.
The charity wound up its operations on Nauru on Saturday, after the Australian government granted the welfare contract to the multinational, Transfield Services.
A recent Senate report outlined allegations of child abuse and sexual assault against Transfield staff on Nauru and found the contractor hadn't been adequately accountable to border authorities.
Save the Children's chief executive, Paul Ronalds, says the end of its tenure means there is no longer an agency to speak up for the rights of children in detention on Nauru.
He says there is a need for greater transparency in Australia's controversial border protection programme.
"The Australian public must know what is being done in their name with taxpayer funds. We need to improve the mandatory reporting of actions against children. We need to have an appropriately funded ombudsman who people can take allegations of abuse to and have confidence that they will be properly investigated."