Google, YouTube, Facebook and MySpace are among 17 social networking sites to sign a European Commission deal to prevent cyber-bullying and protect the privacy of users under 18.
The Commission said the agreement will cut the risks of children harassing peers online and curb "grooming", whereby pedophiles make friends online with children with the aim of seducing them.
Information Commissioner Viviane Reding said in a statement, "It is an important step forward toward making our children's clicks on social networking sites safer in Europe."
Social networking grew 35% in the past year and more than 100 million people are expected to sign up by 2012, the Commission said.
The other social networks to sign up include Arto, Bebo, Dailymotion, Giovani.it, Hyves, Netlog, Nasza-klaza.pl, One.lt, Skyrock, StudiVZ, Sulake/Habbo Hotel, Yahoo!Europe, and Zap.lu.