Three Indigenous children - Evelyn Greenup, 4, Clinton Speedy-Duroux, 16, and Colleen Walker, 16 - disappeared from the NSW Mid North Coast town in 1990-1991.
Evelyn and Clinton's remains were later found in the area.
Greens MLC David Shoebridge, who attended the protest, told SBS News "there's a growing sense in the community that justice needs to be delivered".
A man, who cannot be named for legal reasons, was acquitted of Clinton's murder in 1994 and of Evelyn's in 2006.
Advocates have spent years fighting for the man to be retried, but have been knocked back, including by the High Court in March.
Mr Shoebridge has been pushing to change NSW's double jeopardy law, which he claims would facilitate a retrial of the man and provide "a clear pathway to justice" for the Bowraville families.
A recent upper house inquiry found Mr Shoebridge's proposed changes should not proceed, but said alternatives could be more successful.
Mr Shoebridge said the pressure was now on NSW Attorney General Mark Speakman to act.
"At this stage, it's essential to put some pressure on the attorney general to respond to the inquiry that's just been released and encourage the government to put forward some legislation," he said.
"Day after day, parliament will pass laws that will put more First Nations people in jail. This is the one occasion when the First Nations community has come together and said we would actually like this bit of the law toughened up so we get some justice," he said.
"The fact that we have not been able to achieve that, I find that quite distressing and it does make me pass a harsh judgment on the institution I'm part of, the NSW Parliament."
Additional reporting: AAP