Cyberbullying is a growing problem in primary schools, according to the Anti-Bullying Alliance.
In a small study carried out by the group in south east England, one in five children questioned said they had been bullied online or by phone.
And many of the 227 10 and 11-year olds questioned said they used social networking sites, even though users are meant to be over 13.
Campaigners say parents must learn how to help children protect themselves.
The Anti-Bullying Alliance (ABA), which is a charity bringing together 60 organisations, also released the findings of a survey of parents on cyberbullying at the start of 'Anti-bullying week'.
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