Figures from regulator Ofcom suggest 500,000 five to seven-year-olds are allowed to go online unsupervised.

Teachers have expressed concern many are joining gaming or social networking sites and leaving personal details without realising the risks.

The Child Exploitation and Online Protection centre (CEOP) has devised a cartoon series to warn of the dangers.

In all, 59% of the UK's primary school children use the internet at home, and 8% of those have a webcam.

'Anyone can see it'

"Hector's World" - CEOP's animated series to be shown in schools - features the adventures of Hector the dolphin and his friends as they surf their own "internet ocean".

There are five animated adventures in the series, with each addressing an area of internet safety. As well as warnings, guidance is also offered on how to surf the web safely.

CEOP's head of education Helen Penn said: "We don't want to frighten children but we do want them to be aware of the dangers, so we're using a cartoon character to get the message across.

"Time and time again we come across situations where children have given out all sorts of personal information on the internet without understanding the potential risks.

"They think only their friends will read it, without realising anyone can see it."

The campaign is based on CEOP's "Think U Know" campaign for secondary school children, which it says has reached 1.7m UK youngsters since its launch.

It also comes after pressure from teachers who were concerned about the numbers of very young children using the internet unsupervised at home.

Episodes of "Hector's World" and back-up resources are available online.

Source: news.bbc.co.uk