More and more children in primary schools are being affected by cyberbullying, according to a survey by the Anti-Bullying Alliance.
The group found one in five of the children they questioned had been picked on by phone or online.
And lots of the 10 and 11-year-olds they talked to used social networking sites, even though users are meant to be older than 13.
The group wants parents to learn to help kids protect themselves.
The Anti-Bullying Alliance says cyberbullying is deliberately upsetting someone using things like phones or the internet.
They are worried some people don't take this form of bullying seriously. But they say it can be very harmful, and can cause kids to feel like they can't escape.
One child told campaigners: "I felt that no one understood what I was going through. I didn't know who was sending me these messages.
"I felt powerless and didn't know what to do."
Newsround has made a special programme all about bullying, called Whose Side Are You On?. You can see it on Monday 16 November at 4.55pm on BBC1.