The number of minor assaults on children reported to police has jumped by 40 per cent since hitting a child for "correction" became a criminal offence two years ago.

The latest police report on the effects of the law shows reported minor assaults on children went up from an average of 32 a month in the three months before the law changed to 45 a month in the 21 months after the change.

There are no statistics for the time before the three months leading up to the legislation.

Deputy Police Commissioner Rob Pope said yesterday that the law change's effect on police work had been minimal, representing little more than one in 1000 of the 36,000 offences of all kinds reported a month.

"It continues to be business as usual for us, and police continue to use their discretion and common sense in their decision-making."

Both sides of the argument over next month's referendum on the law claim the police figures support their positions.

Family First director Bob McCoskrie, who helped to gather signatures to force the referendum, said the figures confirmed "non-abusive parents are being investigated - which we always feared".

But Deborah Morris-Travers of the "Yes Vote" campaign, which supports the new law, said they showed it was "protecting those who need it most".

"Police are exercising the discretion affirmed in the law," the former Government minister said. "While the law grants children the same legal protections as all other citizens, police are not prosecuting parents who lightly or occasionally smack their child."

The law change, sponsored by Green MP Sue Bradford, made it illegal for parents to use force against children "for the purpose of correction", but also gave police the discretion not to prosecute "inconsequential" cases.

The police reports show there has been only one prosecution from 33 reported cases of "smacking", and 11 prosecutions from 169 cases of "minor acts of physical discipline".

The single prosecution for smacking since the law change was withdrawn when the primary witness refused to give evidence.

Of the 11 other people prosecuted for "minor acts of physical discipline", three were discharged without conviction, two got six months of supervision, one got nine months' supervision, two were ordered to come up if called upon within six or nine months, one was given police diversion, and two cases were pending.

Mr Pope said the rise in reported child-assault cases reflected increasing public awareness rather than the law change.