A third of parents believe children spend too much time online, and mothers worry far more than fathers about whether certain Internet sites are appropriate for kids, according to a new survey.

Researchers for the nonprofit Common Sense Media and education foundation Cable in the Classroom also found that one in four parents worried that time spent online kept children from exercising or enjoying the outdoors.

Although four out of five parents said the Internet helped their kids in school, nearly three out of four acknowledged that they've had "issues" with their children's online activities, including excessive exposure to advertising or commercialism online and exposure to coarse language, or sexual or violent content online.

Mothers or female guardians seemed most concerned about children's use of the Internet.

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