Momentum is building for a law change to prevent families from stonewalling police when a child has been assaulted or killed.

Public outrage over cases such as the unsolved death of 3-month-old twins Chris and Cru Kahui has thrust the issue into the spotlight, and the Government will soon have a report from the Law Commission suggesting what should be done.

Meanwhile, a senior Christchurch policeman who has overseen child murder cases has put forward his own proposal.

This would see New Zealand follow in the footsteps of Britain, where parents and caregivers who withhold crucial information can be jailed.

On Wednesday, a coroner's inquest in Christchurch heard that the shaking death of 7-month-old Staranise Waru in February 2006 remained unsolved as the child's parents were no longer willing to co-operate with police.

The parents, Nyree Hopa and Robert Waru, repeatedly chose not to answer questions at the hearing into their daughter's death on the basis that they could incriminate themselves.

Justice Minister Simon Power told the Weekend Herald he had asked the Law Commission to speed up a review of the law that dealt with assault, injury and homicide.

"I understand that the commission's soon-to-be-released report includes a new provision to better address situations where it's difficult to identify the responsible offender within the family context and ensure that those responsible for protecting vulnerable children are held to account."

The proposal put forward by Inspector Malcolm Johnston, of Christchurch, is similar to the culpable parenting law in Britain.

The right to silence would be removed, and parents or caregivers would be forced to co-operate with authorities trying to determine how a child has been harmed, and who didit.

Police Association president Greg O'Connor said that while this type of law might not solve a murder, it could provide an incentive for people protecting others to speak up.

Detectives were increasingly being frustrated by situations where people with knowledge of what occurred were refusing to speak, Mr O'Connor said.

Often it was families police dealt with frequently, while lawyers, especially in Auckland, were now advising people who were not even suspects in a crime to keep quiet.

When people were "clamming up", police had to rely on forensic evidence.

"Of course in child abuse [cases], or child in the home, forensics have limited use because obviously the DNA is all over the place."

Children's Commissioner John Angus said he was planning to meet the Law Commission next week on the issue, and did not want to state a "public position" until then. However, he felt equal attention was needed to getting people with concerns about a child's wellbeing to speak out before the child was harmed or killed.