Instead, they are sentenced to indefinite limbo in a camp overseas.

As government ministers Scott Morrison and George Brandis last week trumpeted that all asylum seeker children who arrived by boat and had been held on Christmas Island would be moved to the mainland by early next year, 25 infants remained in detention centres across the country with no hope of being released. Five are held in Broadmeadows in Melbourne's north-west.

Though all were born in Australia and have lived here since birth, under changes to migration law they are considered both "unauthorised maritime arrivals" and "transitory persons". As things stand, none will be released or settled here.

Lawyers and advocates arguing for the babies and their families to stay in Australia say it is galling how little separates them from other unauthorised maritime arrivals now being released into the community.

"It is completely arbitrary," says Katie Robertson, a lawyer with Maurice Blackburn who represents some of the families. "It often has come down to who had a solicitor at the right time and who didn't."

The hard-line policy introduced in the dying days of the second Rudd government dictated that all new asylum seekers arriving by boat after July 19 last year would be sent to Nauru or Manus Island. But not all were.

While some pregnant asylum seekers were sent overseas before they gave birth, others were held on Christmas Island, yet to be sent.

At least 25 in the first group were brought back to Australia to have their babies, or get medical treatment. Most are held in Darwin. Some have been here for more than a year, and some of their babies are old enough to crawl or walk, but – because their mothers were briefly sent offshore – they are not covered by the deal the government made with crossbenchers to release asylum seekers into the community on temporary visas.

The parents were told on Wednesday they and their children – 44 in all, including the babies' 19 older siblings - will be sent back to remote Nauru. They will join about 140 other children in detention on Nauru who will remain there under the recent law changes.

"There is despair and confusion," Ms Robertson says of the families in Australia being sent to Nauru. "People don't understand why they are being treated differently to people who arrived on the same boat – and in some cases in the same family."

Fairfax Media is today publishing pictures with their parents' consent of three babies bound for Nauru. It has agreed not to use their names or their country of origin.

Advocates say the arbitrariness of the decision is illustrated by the case of Aliyah*. Her mother, Fatimah*, and father, Mohammad*, arrived by boat from Indonesia in September 2013, as the Coalition returned to government, along with Mohammad's brother and sister-in-law and their children.

Though Fatimah was pregnant, she and her husband were quickly sent to Nauru. Mohammad's brother and his family were held on Christmas Island for more than a year because they had a three-year-old, who immigration officials considered too young for Nauru. They were recently moved to a detention centre in Adelaide for medical treatment. The administrative decision made shortly after the family arrived in Australia means that half of the family will now stay here indefinitely, potentially on temporary protection visas, while half will go to Nauru.

Sister Brigid Arthur, a Catholic nun and the babies' litigation guardian, says the treatment of asylum seekers is more like a lottery than an ordered, structured process.

"There are always anomalies and contradictions that don't make any sense," she says. "This is a contradiction: to say part of the passing of the bill was to get children off Christmas Island, but then make part of the bill that some children would be sent to Nauru and kept on Nauru.

"I mean, we either have a responsibility to release children from detention, which I believe we do, or we don't."

Fatimah and Mohammad were sent back to Australia after she was diagnosed as being at serious risk of post-natal depression. It was expected she would be here for six weeks, but her health as deteriorated to an extent that she is still here 11 months after giving birth.

Mohammad was present at the caesarean birth of Aliyah, but was sent back to the detention centre shortly afterwards. When Ms Robertson visited Fatimah in hospital a few hours after the birth she found her alone, watched by two security guards.

"She asked if she could hang on to the interpreter who came with me for a bit longer so she could ask the maternal health nurse how to breastfeed," Ms Robertson says.

Four months after giving birth, Fatimah spent a week in a psychiatric hospital. "We got a report from a psychiatrist who said if she was sent back she was at risk of suicide," Ms Robertson says. "The department held her back [from being returned to Nauru], presumably because they decided she was very high risk, but the care she received after giving birth was completely inadequate."

She has now been told she will go back after January 30, when an undertaking by Immigration Minister Morrison to not return the families to Nauru lapses. The undertaking was given while lawyers representing another baby born in Australia but bound for Nauru, one-year-old Ferouz Myuddin, appealed to the Federal Court for him to be granted a protection visa. Lawyers say that case has no standing under the legislation that passed the Senate on December 5.

Each of the families in detention and waiting to be sent to Nauru have their own story. Asylum Seeker Resource Centre campaigner Pamela Curr says one lost a 15-month-old son on the journey to Australia after holding him up in the water for five hours. Another young mother, aged in her 20s, had been living in an African refugee camp since the age of three after her parents fled their civil war-torn homeland. She was assaulted and her life threatened by others in the camp. When she discovered she was pregnant with her fourth child, it was decided she should flee. Her husband and three older children remained in the camp.

Under the amended legislation, Mr Morrison was given greater discretion to push back asylum seeker boats without having to consider what it would mean for the passengers, to conduct fast-tracked refugee assessments that leave little right for appeal, and to block protection claims on character grounds with little explanation.

Crossbenchers concerned about these measures, including Palmer United Party senators and the Motoring Enthusiast Party's Ricky Muir, were persuaded by a promise that asylum seekers on Christmas Island, including all children, will be brought to the mainland and released into the community on bridging visas and be able to apply for the right to work.

The 25,000 asylum seekers Mr Morrison describes as the previous Labor government's "legacy caseload" will also be able to apply for work rights. They may be placed on three-year temporary protection visas, but have been told they will have little chance of qualifying for a permanent visa. They will have no right to family reunion, though Mr Morrison has promised to increase the annual refugee intake from 13,750 to 18,750.

But the new arrangements do not apply to people held in offshore processing centres, including those who have been offshoreand returned to Australia.

Mr Morrison's office did not respond to questions on Saturday. On Wednesday, Attorney-General Brandis told the Australian Human Rights Commission's awards night that 2014 was "the year of releasing children from detention".

He said there were 1992 asylum seeker children in detention when the Coalition was elected, but since then more than 1200 had been released, and that all on Christmas Island would soon be released.

He also said that 2014 was the first year since 2008 when the government could confidently say that no one had died at sea on asylum seeker boats.

Sister Brigid says it is unclear what the government hopes to gain by returning a handful of families to offshoredetention.

"If the government's intention is to stop the boats, they have been stopped. If they're setting out to punish people, surely it's immoral to punish children in this way," she says.

"It is a totally inhumane and cruel decision, and an unnecessary one."

*The names of asylum seekers have been changed.

amorton@fairfaxmedia.com.au