Three-quarters of Europe's children have a profile on a social networking website, while one in five under 13 manage to dodge Facebook's age restriction, a survey showed on Monday.
Some 77 percent of children 13 to 16 years old, and another 38 percent aged between nine and 12, are plugged into a wide range of social networking websites across Europe, said the survey released by the European Commission.
One quarter of them have set their accounts to "public" view, meaning that everyone can see their profiles, making them targets for child predators, the European Union's executive arm cautioned.
Neelie Kroes, the commissioner in charge of Internet issues, called on social networking firms to make the profiles of children only accessible to their approved contacts by default and make them invisible to search engines.
"Growing numbers of children are on social networking sites but many are not taking all necessary steps to protect themselves online," she said.
"These children are placing themselves in harm's way, vulnerable to stalkers and groomers."
The rate of 13 to 16 year olds with social networking profiles is high in western Europe, especially Scandinavian countries: 92 percent in Norway, 89 percent in Denmark, 88 percent in Britain and 82 percent in France.
At 70 percent, the Netherlands is the country with the most children under 13 with a social networking account, with France at the bottom of the list at 25 percent.
The survey, conducted by EUKidsOnline network, found that Facebook is by far the most popular friends-connection website in 17 out of 25 European countries, used by 57 percent of nine to 16 year olds.
Despite an age restriction, 20 percent of nine- to 12-year-old surveyed said they have a Facebook account.
On its private policy page, Facebook says that if it learns that it collected personal information from a child under 13, it will delete it "as quickly as possible."