Smacking kids as young as three can turn them into bullies before they reach school, a new study has suggested.
The research into corporal punishment found that toddlers smacked at least twice a month are at higher odds of being aggressive by the time they are five.
Of the 2500 children studied, almost half were deemed with "higher aggression" and had been spanked more than twice a month.
Regular smacking doubled their chances of adopting bullying behaviours compared with those children who have never been hit.
New Orleans' University of Tulane public health researcher Catherine Taylor said there was growing evidence smacking kids did not work.
"This evidence suggests that primary prevention of violence can start with efforts to prevent the use of corporal punishment against children," News.com.au quoted her as saying.
While experts and most families are divided over whether spanking is damaging, many acknowledge that the occasional spank on the bottom won't permanently hurt a child.
Child psychologist Dr Michael Carr-Greggs said parents should never hit a kid over the head or with an implement.
"The single most effective way to discipline a three-year-old is time out. The second most effective way to modify their behaviour is to notice every time they act in a pro-social way," he said.
Port Macquarie mum, Raylene Alford, uses time out zones and reward charts to discipline her three-year-old son Cameron.
"We didn't want to get into the habit of smacking Cameron when he did something wrong," she explained.
"He responds well to the time-out or naughty step and afterwards we ask him to explain what he did wrong," she added.
A study published in the Pediatrics journal has added to the argument made by many psychologists that smacking can harm children.