PARENTS could let their children change sex without court permission if a landmark legal bid is upheld.

The family of the youngest Australian to receive sex-change therapy is fighting for the decision to be one made between parents and doctors, not the court.

"Jamie", 11, has lived as a girl for years, dressing in female clothing and using the girls' toilets at school.

The court heard she had been diagnosed with gender identity disorder. Her parents said she first identified herself as a girl at age 3.

The Family Court last year approved drug therapy to stop her going through male puberty, but refused to allow later oestrogen treatment.

The parents are appealing against that decision, claiming sex-change treatments should not fall under special medical procedures that courts must approve.

A "public authority" has asked for the right to be heard, arguing the court's role is important and "a potential change in the law may affect not simply Jamie's best interests but the interests of other children with childhood gender identity disorder".

The Australian Human Rights Commission is also involved.

The Full Court of the Family Court agreed both parties should be allowed to appear, saying: "The appeal raises the possibility of a significant change in the law as it now stands and the overturning of many cases."

The Australian Coalition for Equality's Martine Delaney said she could not see why the court had to be involved. "I don't know why it is considered a necessary step," Ms Delaney said.

"You would have to have a hell of a convoluted, strange combination of parents, child and doctor to have a situation where someone was forcing a child into taking those steps.

"I sympathise with the parents on that, in that no parents or doctor is going to make those sort of decisions without a heck of a lot of consideration."

But the Victorian president of the Australian Family Association, Terri Kelleher, said it was a "fraught area" that should be overseen.

"I am just more comfortable thinking there is an independent body, outside those who are very involved in the case, because sometimes your closeness to it maybe doesn't allow you to see the long-term consequences," Ms Kelleher said.

The appeal is due to be heard next month.