As many as 77 per cent of parents aged 25 in a study said they had smacked children, with 12 per cent admitting they severely assaulted a child in the past year.
The data was gathered as part of the Christchurch Health and Development Study and reported in the latest New Zealand Medical Journal.
"The use of physical punishment and more severe forms of physical assault/abuse are relatively common amongst contemporary young parents," the study found.
A separate study in the journal also found that smacking was widespread in the Pacific Island community, and hitting children with objects was common.
Hitting children with objects is in breach of the controversial child smacking law passed this year. A late amendment gave police the discretion not to prosecute complaints against parents where the offence was considered to be inconsequential.
The Pacific Island Families study said that guidelines were needed on what punishments were legally acceptable. The definition of inconsequential offending was unclear.
The studies highlighted the need to target support of at-risk parents, in particular young parents, said Bob McCoskrie, national director of Family First.
He said that the 77 per cent of 25-year-olds who said they had smacked children were not abusing their children when using appropriate and reasonable physical punishment.
"This percentage is consistent with the total number of parents in New Zealand who are using physical punishment in a reasonable and effective way."
A Unicef report released this year also linked poverty, single-parenthood, low maternal education, low maternal age at birth, poor housing, weak family ties, and parental drug or alcohol abuse to violence toward children.
The studies in the medical journal did not establish that smacking should be banned, said Mr McCoskrie.
The Pacific Islands Families study follows a cohort of Pacific infants born at Middlemore Hospital.
The Christchurch study found that the risk of severe physical abuse was greater in lower socioeconomic families and families with a large number of children.
In the group surveyed 37 per cent of 25-year-old parents said they had physically disciplined an infant and 84 per cent said they had physically disciplined a pre-schooler.