Social Reinvestment WA gathered with leaders of civil society organisation on Closing the Gap Day - Thursday - to hand over an open letter signed by more than 1,200 people calling for urgent youth justice reform to Members of Parliament.

The letter called on the Western Australian government to immediately close Unit 18 and implement the recommendations of the Coronial Inquest into the death of 16-year-old Cleveland Dodd.

In Western Australia, Aboriginal and Torres Strait Islander children make up 63 per cent of those in detention, despite representing just 4.4 per cent of the population. Unit 18 has disproportionately held Aboriginal children in harmful conditions, and two Aboriginal young people have died by suicide in youth detention in WA.

The Coronial Inquest into Cleveland Dodd's death found that systemic and institutional failures contributed to a preventable tragedy.

Signatories to the open letter called for urgent action to ensure no more children die in the care and custody of the WA government.

Members of Parliament who accepted the handover included: Shadow Minister for Aboriginal Affairs Neil Thomson MLC; Shadow Minister for Police, Corrective Services and Youth Adam Hort MLA; Jess Beckerling MLC; Julie Freeman MLC; and Tim Clifford MLC.

Invitations were also sent to the Minister for Aboriginal Affairs, Don Punch, and Minister for Corrective Services, Paul Papalia, but they declined to attend or send a government delegate to receive the letter.

Nadene Dodd, mother of Cleveland Dodd, said she does not want another family to suffer the loss of a beloved child in custody.

"I still want Unit 18 closed," she said. "I don't want anyone to go through what I went through. The government needs to act on the Coroner's recommendations now and stop wasting time."

Sophie Stewart, CEO of Social Reinvestment WA, said the open letter has been signed by more than 1,200 Australians, including leaders of civil society, former Federal Ministers, a former WA Premier, a former President of the Children's Court, and Australians of the Year.

"We are united in calling for the implementation of the Coroner's recommendations following the death of 16 year old Cleveland Dodd, and for the closure of Unit 18," she said.

"It's been almost four years since Labor opened Unit 18 'temporarily'. Two years since Cleveland's death inside. And over three months since the Coroner handed down findings that systemic and institutional failures contributed to a preventable tragedy. This government has yet to commit to the implementation of his expert recommendations- and the cells in Unit 18 still hold WA kids. We cannot wait until 2028.

"Western Australians expect more and kids like Cleveland deserve better from the government who represent us, and the institutions our tax dollars pay for."

Ronald Bin Swani, Advocacy Lead at Social Reinvestment WA, said it was disappointing WA Labor sent no one to meet the delegation presenting the letter, "but are bolstered by the commitment from across party lines that saw the Greens, Liberal, and National parties come to receive our letter".

"It's a commonly shared sentiment that no more children should die inside our prisons- and government must act to prevent this," he said.

WACOSS chief executive Louise Giolitto said if the WA government wants to reduce suicide and youth incarceration rates among Aboriginal and Torres Strait Islander peoples it must "invest in what works, including justice reinvestment and community-led solutions that prevent harm rather than sending children into adult prisons".

Kylie Wallace, CEO of the Youth Affairs Council of WA, said Cleveland's death was both "predictable and preventable".

"Unit 18 was never safe for children, and every day it remains open is a decision to continue that harm. We're calling on the WA Government to close Unit 18 now and invest in community-based, Aboriginal-led supports that actually keep children safe," she said.

"The Youth Affairs Council of WA calls on the State Government to implement the Coroner's recommendations. It is unacceptable that two young people have lost their lives in the justice system.

"We must invest in prevention, early intervention and diversionary programs that support children and young people in their communities."

The Honourable Fred Chaney AO, Former Federal Minister for Aboriginal Affairs and Senior Australian of the Year, urged Roger Cook to act.

"I ask the Premier to act on what he knows need to be done. Close Unit 18... it's inhumane. It's inhuman," he said.