About $30 million will be spent re-developing the state's first designated children's court, which closed 32 years ago.

The Surry Hills site will be used to replace Bidura Children's Court building at Glebe, which was sold by Government Property NSW for $33 million last year to private developers.

Designed by prominent government architect Walter Liberty Vernon, the federation-style historic facade will be preserved in the renovation which will be carried out in consultation with heritage authorities.

The NSW Children's Court president, Judge Peter Johnstone, said he was excited about the development, which would include four new courtrooms, AVL technology and a private room for vulnerable witnesses to give evidence via closed-circuit cameras.

"The beauty of it is it's keeping the best of the old and creating the best of the new … it's a lovely old facade."

"The Glebe location [Bidura] was very inconvenient and hard for people to get to. The building was horrible and at one stage you couldn't even get mobile phone reception," he said.

The walls of the old holding cells at Albion Street are covered in graffiti and tell the tales of many who were kept down there between 1911 and 1983.

It was rare for children to be held downstairs but often men were locked in cells for failing to pay maintenance to their wives.

When the court first opened in 1911, Surry Hills had a population of 30,000 and many of its residents lived in poverty.

The court complex, on the corner of Albion and Commonwealth streets, also housed a boys' shelter, where children were kept before their court cases.

But from 1913, boys were being remanded for up to weeks at a time for crimes such as joyriding, petty theft, truancy and failure to attend military training.

Rod Blackmore, 80, is the former chief magistrate of the Children's Court and presided over matters in the complex from 1977 until its closure in 1983.

His father and grandfather also presided over matters at Albion Street.

Mr Blackmore said the way children were treated by the justice system had changed significantly from a time where children were seen and not heard and often had no legal representation.

Standing in the court complex last week he said he had "mixed emotions" about the redevelopment but said Surry Hills was not the "sordid" suburb he once remembered.

"There was a report done in 1936 that criticised both the building and its location. They said it's strange you would put up a building to do uplifting work with children in such a sordid location as Surry Hills," he said.

Judge Johnstone agreed the area had changed, as had the nature of juvenile crime in recent years.

He said he believed children were committing crimes at a younger age and the crimes they were committing were more violent.

"I think it's the influence of social media, video games, television," he said.

"We are also starting to see 10- and 11-year-olds committing violent crime and we are also seeing [more] girls committing more violent crimes.

"Our job is to get them through that adolescent period as unscathed as possible, keep them out of detention, prison and remand with a view to getting them into the community as useful, productive citizens."

NSW Attorney-General Gabrielle Upton said the renovated site would make accessing justice easier for vulnerable children.

"The children and young people who come before the Children's Court are often some of the most vulnerable members of our community. They need our care and attention," Ms Upton said.

"This major upgrade will ensure they get access to fast, fair justice which will help reduce the stress of being part of the justice process."