A four-year-old child who identifies as transgender has begun to transition before their first day of kindergarten.

The child, who is unidentified for privacy purposes, is part of the Safe Schools program and hopes to complete the gender transition by next year. 

But psychologists have questioned whether the preschooler is too young as gender transition among young children skyrockets, according to the Daily Telegraph.

The Education Department would not reveal whether the child was born a boy or girl. 

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While the four-year-old is the youngest Australian on record changing their gender, hundreds of other children and their parents have sought advice from the gender dysphoria unit.

The Westmead Children's Hospital in Sydney has had referral patients at its gender service department triple.

'We have a number of students who are going through gender transition in our schools, with the youngest being a four-year-old at the moment,' the Educations Department's deputy secretary of school operations Gregory Prior said.

However 250 children - some as young as three - have made appointments with the gender dysphoria unit at Melbourne's Royal Children's Hospital.

But just 10 years ago the unit had only logged one young patients.

'There is a huge difference between dress-ups and a child believing with every fibre of their being they are in the wrong body,' child psychologist Michael Carr-Gregg told The Daily Telegraph.

But Australian of the Year finalist and transgender advocate Catherine McGregor said she would be concerned an 'irreversible' decision could be made as the children are so young.