"What the numbers are indicating is that things appear to be flattening out a bit and in some areas, particularly emotional abuse, they seem to be dropping a bit," he said.
"Obviously at this stage it's very early, and they are relatively small numbers, so I think what we would want to do is to investigate it further and do some analysis of why that is happening."
But he said two things gave him more confidence that the drop may be more than just a statistical blip.
First, the drop in substantiated cases came despite a continued increase in notifications to CYFS of suspected abuse and neglect - up from 150,747 to a record 152,800 in the latest year, including an increase in police referrals of children in homes where domestic violence occurred from 57,153 to 62,678.
CYFS also investigated more cases - up from 57,949 to 61,074.
"So we have investigated more cases but found slightly less child abuse," Mr Nixon said.
Second, the drop in substantiated child abuse matched a "levelling off" in family violence offences reported in police statistics for last year.
"Most of the children who have a substantiation around emotional abuse do so where there is a situation of domestic violence, so if there has been a drop in domestic violence reporting it would follow that there may be a drop in emotional abuse substantiations," he said.
But the co-director of the NZ Family Violence Clearing House, Dr Janet Fanslow, said both CYFS and police data were affected by changing policies and priorities and could not be used to indicate underlying trends.
"While we would love the story to be true, and it's what we are all working towards ... we don't have the data sources that are sufficient to draw that conclusion," she said.
The figures show slight falls in emotional abuse and in sexual abuse, but continued small increases in findings of physical abuse and of neglect. Findings of physical abuse are still 74 per cent higher than in 2003-04.
New Zealand had the sixth-highest rate of child deaths from maltreatment in a Unicef league table in 2003.
An update in 2007 found that the total death rate from accidents and injuries of children under 19 was higher in New Zealand than in any of 23 other rich nations.
A white paper setting out Government plans to deal with the problem is due on October 12.