The number of New Zealand parents who say they do not smack their preschool children has doubled in the past 12 years, suggesting the practice is becoming socially unacceptable.

A national survey of 612 parents and 539 caregivers with children aged five and under has found that 49 per cent of parents had not smacked their children in the past three months or used physical discipline as a way to handle misbehaviour.

A survey in 1993 found only 25 per cent of parents with under-six-year-olds, and a mere 11 per cent with children aged two to four, had never used physical punishment on under-fives.

The author of the 1993 study for the Commissioner for Children, Dr Gabrielle Maxwell, said the swing away from smacking in just 12 years was "amazing".

"I think the campaign against it has had a lot to do with it. There has been public debate, and there has been a real buy-in by parents to finding other ways. It's very pleasing."

The latest survey was conducted by Auckland's Gravitas Research for the Ministry of Social Development's three-year, $10 million public education campaign called "Strategies with Kids - Information for Parents" (Skip).

Prime Minister Helen Clark said last year that the Government would wait to see the effects of the campaign before deciding whether to repeal section 59 of the Crimes Act, which allows parents to use "reasonable" force "by way of correction towards the child".

A Herald poll in October 2003 found that 70 per cent of New Zealanders supported the present law, and other surveys have found support levels of up to 80 per cent.

But the Gravitas study has found that in practice parents are increasingly avoiding smacking even if they still believe they should have the legal right to do it.

The researchers asked parents and caregivers of children aged five and under which of 10 methods they used to deal with a child's misbehaviour, ranging from "ask them not to do it again" to "physically discipline the child, for example, smack the child".

Forty-five per cent of the parents, and 20 per cent of grandparents and other caregivers, said "physically discipline the child" was one of the methods they used.

The remaining 55 per cent of parents and 80 per cent of caregivers were then asked whether they had actually physically disciplined a child in the previous three months. This raised the total of those who either used physical discipline as a method, or had used it in the previous three months, to 51 per cent of parents and 21 per cent of caregivers.

Half of those who said it was one of their methods said they had not actually used it in the previous three months.

Two-year-olds were most likely to be smacked, and physical discipline became less likely as the children grew older and better able to understand verbal instructions.