Bridgette "Biddy" Porter was killed by a teenager in northern NSW in July 2020.
The 10-year-old's killer, found not criminally responsible due to mental illness, cannot be identified due to multiple legal restrictions.
Details of the injuries Biddy sustained during her death are also banned from publication.
But her parents want scrutiny of the legal system, which they say has restricted their ability to speak or access information about their own daughter's death, while protecting her killer.
They are also advocating for better support for victim's families as they continue to deal with severe anxiety and complex post-traumatic stress disorder.
"We know that nothing we can ever do will bring our little girl back to us," parents Rebekah and Dominic Porter said in a statement.
"But in her memory, we hope to help other parents of murdered children by doing what we can to encourage a judicial system that is fair, transparent and accountable to the community it exists to serve, while increasing the level of essential funding and support services for victims' families."
They are petitioning for parliamentary inquiries into how prosecutors handled the case, as well as the state's Mental Health Review Tribunal, which they say lacks accountability and transparency.
They also want reforms to victims' services, increasing support beyond the $7500 they each received, and an inquest into their daughter's death.
The petition has been supported by Advocacy Australia, whose chair Clare Collins said families of victims of serious crime needed more support.
"There appears to be inequity between a victim's rights compared to those of a killer," she said.
They get no free independent legal support to evaluate recommendations prosecutors may make to finalise a matter, or represent them at hearings before the mental health tribunal, she said.
Victims will continue being silenced and denied justice if prosecutors and the tribunal are not investigated, Ms Collins said.
"No public servant or service should be above public scrutiny," she said.
Independent state MP for Orange, Phil Donato, also supports the petition.
"The devastating impact of Biddy's heinous killing is compounded by what her parents believe to be a gross miscarriage of justice and a significant lack of appropriate support services," he said.
Attorney-General Michael Daley has been contacted for comment.
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