Most parents believe social networking sites such as Facebook and Twitter are making teenage web surfers "dumber", cyber-safety research in Australia revealed on Sunday.

About 65 per cent of parents with children using social media say it distracts them from their homework, said the report commissioned by Australian telecom and information services company Telstra.

A quarter of parents say their teens spend more than seven hours a week connecting with friends online, while less than 40 per cent of parents fear this behaviour affects their children's well-being.

The study, conducted by Newspoll, reveals 84 per cent of teenagers in the 14-17 years age-group use social networks, and about half of children between 10-13 years use sites such as Facebook.

Small changes, such as placing computers in a common area instead of in the children's room, and setting time restrictions on social media usage, help keep teens focused on their studies, said cyber-safety expert Dr Martyn Wild.