Police regularly witness an increase in cyber bullying among children when they're off school. "During school holidays kids have more access to, and more time with, the technology," NSW Police Acting Commander of Operational Programs Steve Johnson said.

Australian Primary Principals Association president Dennis Yarrington said students often felt freer to cyber bully during the holidays because they didn't have to turn up to school on Monday and face the consequences of their actions.

"There is potentially less supervision ... Students feel they can make comments without necessarily being followed up," he said. "In the holidays who do kids go to [if they're being bullied]?"

Mr Yarrington said kids also mix with different groups during the holidays, which can create more opportunities for fallings-out, sharing of online details with strangers and inappropriate use of social media. Bullying escalates far more quickly online than in the physical world.

One in five children aged eight to 17 experiences cyber bullying, according to the Federal Department of Communications. Children aged 11 to  14 are the most vulnerable, as they transition from primary to high school. They are being granted more independence, often given their own mobile phone, but may not have the maturity to foresee the consequences of their online actions.

Cyber bullying is any information posted online which threatens, intimidates, harasses or humiliates a child.

Cyber bullies might set up fake social media accounts in their victim's name, take over their victim's social media accounts, or upload photoshopped images. They may also send abusive texts and posts, repeatedly send unwanted messages, or circulate images online without the subject's permission.

"Internet harassment is pervasive and 24/7," Children's eSafety Commissioner Alastair MacGibbon said. "It's very damaging to people's reputations and their sense of social security. It really impacts them psychologically and can cause them dreadful harm."

Mr MacGibbon has seen "slut shaming" web sites that post the names of girls from a particular area, and an interactive map showing where they live. Other cyber bullying which has occurred includes "vicious" outing of someone's sexuality and posting of nasty videos threatening to harm or kill someone.

There is no hard data available on cyber bullying trends in Australia, as the Office of the Children's eSafety Commissioner has only been operating since July, and police say it is often under-reported. Cyber bullying, online harassment and stalking account for one in 10 complaints made to the Australian Cybercrime Online Reporting Network since it was set up a year ago.

Parents who believe their child has been cyber bullied are encouraged to approach the social media company and ask them to take the offending material down. If that doesn't happen within 48 hours, they can then complain to the eSafety Commissioner who has the power to force companies to remove the offending material.

"We're trying to empower families and remove the [assumption] that nothing can be done," Mr MacGibbon said. "Mostly what children and families want is to make the material go away. We take down harmful material which then gives them breathing space."

Parents can also go to the police with evidence of cyber bullying. Acting Commander Johnson said: "Online bullies think they can be anonymous, but police can track them down."

Parents are advised to be aware of what their children are doing online during the holidays, and keep computers and tablets in the living room or kitchen where they can be monitored.

"We encourage parents to keep an eye on what kids are doing on social media and the Internet – not looking over their shoulder, but asking how they're going, is everything OK," Mr Yarrington said.