The Administrative Tribunal has been flooded with appeals against bans issued by the Office of the Children's Guardian under strict laws introduced last year.

Six out of 10 cases decided by the tribunal in the past six weeks were found in favour of men who had been forced out of the family home or prevented from working after failing a check.

In at least two cases carnal knowledge convictions recorded against men 40 years earlier when they were teenagers and in a relationship with an under-age girlfriend caused them to fail the Working With Children Check.

One such man, now caring for his grandchildren, continues to be in a relationship with the same woman, who was pregnant with their first child at the time the crime was reported to police by a third party.

A gay youth worker who failed the check because he had downloaded a "fake nude picture of celebrity Justin Bieber" to his computer, amid a Twitter scandal, was also among two dozen cases considered by the tribunal this year. Eleven bans have been overturned.

Psychologist Christopher Lennings, who prepares reports for the tribunal, says there has been a spike in cases because the law was changed to require foster parents and kin carers to undergo a check for the first time. Decades-old convictions are triggering the bans and it is having "severe impacts" on families.

"The dragnet has broadened," Mr Lennings said.

"Fathers, foster fathers and grandfathers will have to leave the family home. It has significant impact on the attachment with the children, who have been involved in a strong relationship with a potential offender and can no longer have contact or must have supervised contact.

"It has a significant impact on the carer parent who suddenly becomes a single parent. There is significant financial impact in having to run two households instead of one household."

The husband of a woman who had run a family daycare service in their home for more than a decade failed the check because of a carnal knowledge charge more than 30 years earlier, for which he had been fined $250. Parents of children in the daycare service wrote letters in his support and the bar was overturned.

A spokeswoman for the Office of the Children's Guardian said all of the cases overturned by the tribunal involved an offence that automatically disqualified the person under the new law.

"It is then a matter for the tribunal to consider whether the applicant has discharged an onus to demonstrate they do not pose a risk to the safety of children," the spokeswoman said.

Family and Community Services Minister Gabrielle Upton said: "I am satisfied with how the Working With Children Check is working and importantly that there is oversight of it through the tribunal."

Ms Upton said the check was an "important way to ensure the safety of children".

In the case of the man barred from working after downloading a fake picture of pop singer Bieber, a local court had determined the single digitally-altered image was child pornography and placed him on a good behaviour bond.

"The Children's Guardian was legislatively required to refuse a Working With Children clearance," said the spokeswoman.

The bar was overturned by the tribunal.

Another man, convicted of rape in the 1970s, had his bar overturned to enable him to continue caring for a large number of grandchildren, whom he and his wife housed, fed and took to school each day. Appeals require details of old offences to be re-examined and the applicant to be pyschologically assessed.

Mr Lennings said the law meant the men are "forever under scrutiny".