An international expert in early childhood told a conference in Melbourne Saurday many pre-school teachers failed to respond adequately to bullying behaviour by three and four-year-olds.
"Pre-school teachers who do not intervene at all and just think it's part of playing can affect a child for life,'' said Ester Ng.
"If the behaviour is not controlled, by the time these children go to primary school they will have mastered the skill in bullying in a more aggressive way.''
Speaking at the National Coalition Against Bullying Conference, Ng said preschoolers often used group power to exclude a child from a game - or a more confident child would snatch toys from a vulnerable one.
She said, unlike previous generations, these children were far more bold in their expression.
"They say what they think. Pre-school teachers say they do it discreetly, they either use an elbow or hand to push someone away and they are only three-years-old.''
Ng called for early childhood teachers to be better trained to identify and discipline potential bullies.
She said how a preschool teacher responded helped determine if the child would master the skills of excluding or picking on someone - or targeting a weaker one.
A separate Australian study found that pre-school teachers tended to be ambivalent about the category labels of "bully'' and "victim.'.
It is estimated one in seven students will experience bullying, either as a victim or as a perpetrator.
Sherelle Kozarovski, childcare manager at the Betty Spears Child Care Centre in Tempe, said bullying existed in all age groups.
"Babies and toddlers without language skills sometimes bite one another, while older children name-call or say things like: 'You can't play here','' Mrs Kozarovski said.
Under the centre's anti-bullying policy, children are taught to use positive words instead of harsh language and hitting or kicking.
A child may be removed from the group for "time out'' if the behaviour continues.
"We try to empower them by giving them the language and the confidence so, when they go to school and there are not so many teachers around, they have the skills to stand up for themselves,'' Mrs Kozarovski said.