The law is to be changed so that adults who do not intervene when a child in their home is at risk of death, serious injury or sexual assault will be held legally liable.
The recommendation is contained in the Law Commission's latest report into the Crimes Act, which focuses on provisions dealing with crimes against the person.
The commission says it is entirely unacceptable that the current law imposes no legal duty on an adult to protect a child in their home.
Justice Minister Simon Power says the new law will ensure it is no longer an excuse to say you were not directly involved in abusing a child: if you're living in the house and you know or knew abuse was going on, that will be enough to make them liable.
Children's Commissioner John Angus says that in cases similar to that of the three-month-old Kahui twins, where murder or manslaughter can't be proved, someone could still be held accountable.
The proposed changes which Mr Angus says will help combat New Zealand's poor record on child abuse, will be introduced to Parliament in legislation early next year. They will also apply to vulnerable adults.
Other reforms include strengthening liability for offences involving cruelty to a child. At present, a person cannot be found guilty of that offence if it is found that they acted out of ignorance or thoughtlessness.
The commission proposes replacing that defence with a gross negligence test, viz, a jury would only have to find that the behaviour was a major departure from the standard of care expected of a reasonable person.
The commission recommends that the maximum penalty for that offence be doubled from five years in prison to 10.
There are also proposals to simplify the way charges are laid for assault, serious injury and homicide.