UNICEF says Australia is violating the rights of the child by sending refugees in Nauru to Cambodia under a controversial 30 million US dollar resettlement deal.
The first refugee is expected to be flown from Nauru to Phnom Penh this week.
UNICEF's East Asia and Pacific Regional Director Daniel Toole says no government policy or action should knowingly put children's lives or wellbeing at increased risk.
He says according to the Convention on the Rights of the Child, to which Australia and Cambodia are parties, the rights of children must be guaranteed.
He says the governments have a clear responsibility to protect children's rights in every circumstance.
Mr Toole says any government that takes actions which will increase the risks children face must accept a special responsibility for safeguarding their rights.
Meanwhile, Australia's Refugee Action Coalition has expressed concerns for three newborn babies that are due to be transferred to Nauru with their families, from Darwin.
Ian Rintoul says more than 20 people from three families as well as three single men have been transported to Nauru, in a move he says is a breach of an understanding brokered with the Immigration Department that no families would be transferred.
Mr Rintoul says he is concerned for the welfare of the babies who will be expected to survive in the same tents as their families, in the heat, humidity and water shortages of detention centre.
He says the three babies are three more reasons to protest for an end to offshore processing.