Australia's fast-growing number of transgender children are facing an alarming risk of suicide, self-harm and depression, due to a costly legal obstacle to treatment.

Parents, health professionals and legal sources are calling for the laws to be changed to protect this already vulnerable group.

At present, parents of teenage children seeking second-stage hormone treatment must apply to the Family Court of Australia, regardless of agreement between the child, their family and a medical team, which includes a psychiatrist.

The legal process is extremely costly and can involve long delays, which threaten the effectiveness of the time-sensitive treatment.

Sarah*, the mother of a young transgender girl who will soon apply to the court for approval to have stage-two treatment, said the process typically costs families up to $30,000.

"Kids are hurting themselves and suiciding because they cannot access treatment because the justice system is making it impossible for them to get it," she said.

After a legal appeal two years ago, families no longer need apply to the court for stage-one treatment, called puberty blockers, but must get court approval for stage-two, or cross-changing hormones. Stage one is fully reversible and stage two mostly reversible.Children typically have stage-two hormone treatment at around age 16, to promote the development of physical changes associated with the gender they identify with.

Sarah said families she knew had "nearly gone to the wall" trying to afford the legal costs of getting treatment - some even looked to the black market for drugs.

"The pressures on families are monumental," she said. "It's not just a case of loving parents accepting their transgender child and having a few challenging conversations with people who disagree or a school that's reticent to help. It's profound discrimination within the system."

Marco, a young transgender woman who volunteers at two support groups for transgender children and young people, said she had seen several families in deep distress over the legal situation.

Medical professionals have supported the call for legal reform. Associate Professor Campbell Paul of the Royal Children's Hospital Gender gender dysphoria clinic agrees the current legal requirement is putting adolescents at risk.

"For any family it's a very significant undertaking to go to the Family Court, with considerable cost and delay. It can be very distressing for the young person and there is a risk of self-harm, and feeling that life is worthless."

Associate Professor Paul, a consultant psychiatrist, said the clinic had a long waiting list - children can wait months for an appointment.

The RCH clinic,  a multi-disciplinary team including mental-health and adolescent-health specialists, is the only one in Victoria and has noted a huge rise in the number of transgender children, from two children in 2003 up to 104 in 2014.

There is also support in the legal community for change. A spokeswoman for the Family Court says it is aware the delays in the process are a cause of concern for all involved.

The Family Court is working on a new process for these cases, including a specific application form. It aims to reduce the waiting times involved.

Associate Professor Paul said it was extremely rare for children to no longer feel their body did not match the gender they identified with, once they had moved through puberty.

He said the clinic had worked with children and families over a long period. "A lot of what we are trying to do is help children and adolescents feel confident and comfortable to express who they are."

*not her real name