Ministry of Education deputy secretary of regional operations Katrina Casey said: "The ministry received a complaint following an incident involving a child at a South Auckland ECE centre.
"The ministry is supporting staff at the centre who are working with parents and children to ensure a safe and secure learning environment."
Casey refused to provide details of the attack - citing privacy concerns - but said the ministry had not received any other similar complaints this year. Details released under the Official Information Act reveal the youngest child to be stood down from school last year for assault was 5 and the youngest to be suspended was also 5.
However, South Auckland social workers say they are dealing with troubled children aged 3 and 4 who are strangling classmates and stabbing them with scissors.
ChildForum chief executive Dr Sarah Farquhar says the ministry is unlikely to have a full picture on the level of violence in preschools because early childhood centres are not required to report incidents to the ministry.
"I believe that it would be helpful if the ministry collected information on exclusions and suspensions and used this to identify services with the highest rates of exclusion so professional support can be given to teachers and services will be less likely to push for children to leave."
Recently released 2011 figures from the Ministry of Education show stand-down rates of misbehaving students continue to fall but education experts and teachers say there is an increasing number of children who are difficult to handle.
South Auckland psychologist Barry Kirker said most violent children were too young to be called psychopaths.
"For them to be strangling or stabbing each other it's not genetic, it's not a behaviour you're born with. To get the idea to do that they'd have to have seen it somewhere."
He said he knew instances where children had been kicked out of preschools for violent behaviour.
"I know that for a fact. They're told to leave and find another centre."
Principals' Federation national president Phil Harding said he was increasingly concerned about the number of children acting out violent and sexual fantasies at school.
• Do you know of any serious incidents at a preschool? Email editor@hos.co.nz.