A leading specialist in child protection estimates 10% of New Zealand children are brought up in abusive households.

The comment was made on Tuesday at the inquest in Auckland into the deaths of Cru and Chris Kahui, three-month-old twins who died from traumatic head injuries in 2006.

A child abuse specialist at Starship Hospital, Patrick Kelly, said he supports the introduction of mandatory reporting of child abuse by health and education authorities.

He said the law needs to be changed so there is a lower threshold of injury required before cases are referred to Child Youth and Family.

And Dr Kelly also told the inquest doctors and nurses need more training in how to spot cases of abuse.

Also at the inquest, medical experts said brain damage suffered by the Kahui twins could have come from being dumped into their cots.

The inquest resumed on Monday after a seven-month adjournment.

Their father, Chris Kahui, was acquitted of their murder following a High Court trial in 2008.

Three paediatricians and a pathologist gave evidence on Tuesday about how the babies died.

They agreed the twins might have suffered their injuries from being dumped on their mattresses.

They said it was possible the boys had been put down forcefully, but it was more likely they were slammed down.

Earlier, the coroner was told that Chris had a fractured skull and Cru had tears to his brain's cortex.

An Australian pathologist, Professor Roger Byard, has told the coroner the post-mortems could have been more extensive, with more detailed examinations of the boys' eyes and ribs.

Dr Kelly said post-mortem practices had improved at Starship since 2006.

But he said there still are not enough paediatric pathologists in New Zealand.