(CNN) -- Status updates, photo tagging and FarmVille aren't just for adults or even teenagers anymore.

Researchers say a growing number of children are flouting age requirements on sites such as Facebook and MySpace, or using social-networking sites designed just for them.

Facebook and MySpace require users to be at least 13. But they have no practical way to verify ages, and many young users pretend to be older when signing up.

Some scientists worry that pre-adolescent use of the sites, which some therapists have linked to Internet addiction among adults, could be damaging to children's relationships and brains.

But many other experts say there's not any solid research to back that up and that most children seem to use social-media sites in moderation, and in positive ways.

"For the most part, although there's so much press about all the bad things they're doing, much of what they do on these sites is stuff they would be doing anyway," said Kaveri Subrahmanyam, a professor of psychology at California State University-Los Angeles.

In two surveys reported this year by Pew Internet Research -- of 700 and 935 teens, respectively -- 38 percent of respondents ages 12 to 14 said they had an online profile of some sort.

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