Protesters have rallied outside NSW parliament to demand justice over the unsolved murders of three Aboriginal children in northern NSW 23 years ago.

Around 100 people marched from Hyde Park to parliament house on Thursday, stopping traffic as they called on Attorney-General Greg Smith to reopen the cases and for a judicial inquiry.

Colleen Walker, 16, Clinton Speedy, 16, and four-year-old Evelyn Greenup disappeared from the Bowraville community over a five-month period in 1990.

In 1991, local man Jay Hart was charged with the murder of Clinton and Evelyn, but was acquitted of murdering Clinton in 1994.

Soon afterwards prosecutors also dropped the charges relating to Evelyn.

After an inquest into her death in 2004, Mr Hart was once more charged with Evelyn’s murder and again acquitted.

The families of the victims continued to push for a retrial, prompting Mr Smith to agree to review the case in 2011.

But in February this year he announced his decision not to consider new charges.

Ronella Jerome, Clinton Speedy’s aunt, said on Thursday that the initial police investigation was mismanaged, highlighted by a subsequent coroner’s inquest.

“Police failed our children, the legal system failed our children … we deserve our day in court and we will never give up,” she told reporters.

Clinton’s nephew, Elijah Duroux, said the case was part of an Australia-wide pattern where Aboriginal deaths were not subjected to the same rigorous legal investigation.

“I guarantee if it were three white kids on the North Shore or some other posh place around Sydney, justice would have been served on a silver platter,” the 15-year-old told reporters.

Greens MP David Shoebridge has a motion before parliament calling for the families to be heard by a parliamentary committee.