That can lead it to throwing weight behind parents who don't deserve it and in so doing mislead the public, he told Radio New Zealand today.
In one case a parent prosecuted for hitting a child with a pillow "at face value ...an extreme over-reaction" turned out to have more than 70 convictions for violent offences.
A review report by Police Commissioner Howard Broad, Social Development Ministry chief executive Peter Hughes and Mr Latta was released yesterday, saying they had found no evidence police or welfare staff were reacting inappropriately.
The law as it stands bans smacking for the purposes of correction, but police have the discretion not to prosecute for inconsequential smacks.
Mr Latta reviewed several individual cases highlighted in the media by opponents of the law.
He said he was personally reassured the law change made no difference to the way the police and social workers did their job.
Family First forwarded cases to Mr Latta, In all of them he felt Child, Youth and Family and police behaved in an appropriate fashion.
Family First spokesman Bob McCoskrie rejected any suggestion it had been misled.
It had not relied simply on what prosecuted parents told it, but in some cases had provided the police statement of facts, and sentencing notes.
Despite the review finding the opposite, he still did not accept the law was working.
He said the review didn't look at effect of the law on the general confidence and psyche of parents, or whether children felt parents now had less power over them.
His "general feedback" indicated there had been changes in parenting.
Both he and ACT MP John Boscawen told Radio New Zealand they could find minor cases where parents had been prosecuted.
The Government has said it will not change child discipline laws, with Prime Minister John Key reassuring parents they won't be prosecuted for a light smack.
Mr Key said the law was working the way Parliament intended, and again said he would change it if parents were prosecuted for lightly smacking their children.
He was asked at a press conference whether he was saying it was acceptable to lightly smack a child.
"Yes, I think so," he replied.
"It's up to individual parents to decide how they're going to parent their children. My view is that it will depend on the circumstances and how you want to raise your child."
The review report contained several recommendations, including establishing a helpline for parents who were approached by authorities about smacking their children.
Mr Key said the recommendations would be implemented.
Family First said if so many support mechanisms were needed to ensure the law worked, then it needed changing.
