The Child Exploitation and Online Protection Centre (Ceop) has launched a new online safety programme aimed at five to seven year-olds.
Recent research from Ofcom found that 59 per cent of children in this age bracket access the internet at home, and 21 per cent do so unsupervised.
The launch builds on the existing Thinkuknow education initiative, which Ceop reckons has already reached over 1.7 million young people between the ages of eight and 16 years.
Ceop is now reaching out to parents of much younger children with vital 'safety first' advice through a series of cartoons featuring Hector the dolphin.
Hector's World comprises five animated episodes which explore issues such as personal information, trustworthiness, making positive choices online and how to be open with a trusted adult when they use the internet.
"Recent research, coupled with feedback from our own youth panel and our work with parents, shows that children are exploring the online world from as young as five years old," said Jim Gamble, chief executive of Ceop.
"Teachers have asked us for this material because it is never too early to start giving children 'safety first' messages.
"In the same way that we teach small children to cross the road safely, there is a need to ensure that young children learn good habits for a future life online."
Hector's World has been adapted for a young UK audience following a successful run in New Zealand. It is backed up by a collection of free resources available to parents and teachers via the Ceop education website.
All material has been developed in consultation with teachers and the government's education technology agency Becta.
"We face a careful balancing act when it comes to young people online, no matter what their age," said Niel McLean, executive director of Institutional Workforce and Development at Becta.
"We should definitely encourage their enthusiasm to embrace the opportunities the internet offers but we must also ensure that they explore and develop their skills in a safe way."
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