It seems to be taken as absolute truth that there is such a thing as harmful information. This has at various times been presumed to come in the form of comic books, rock and roll, a wide variety of television shows, video games, pornography (child or not), and Beethoven, among everything else "kids today" are doing or express an interest in. Really, read anything mainstream about the Internet or video games and you'll see that it's a foregone conclusion: information is dangerous.
Now, that might be just rampant anti-intellectualism, which is perhaps worth a good rant in its own right. Misinformation can be harmful (bad medical information for instance), however the people who propose that we need to protect children from information have obviously not been struck by the irony that the idea that information is harmful is the only harmful idea. I think this is perhaps a more modern expression of the concept of freedom of speech.
Anyway, under the assumption that there is deadly harmful information out there, I assumed that surely Google would be able to point me to it. Surely some joker would have put together a web page of fully weaponized information. The first hundred or so search results would seem to indicate that this has not happened. There is lots of presumption going on there that such information exists and that people (particularly children) need to be protected from it, but there is no information to be found about what this information actually is, or by what mechanism it is actually harmful.
So, what is "harmful information" then? It could be information that diminishes authority (of parents over their children, or governments over their citizens). It could simply be information that parents find uncomfortable discussing with their children. Both of those things are only harmful to the self-important delusions of those worrying about it, though, not the subject of such "concern."
OK, I'll admit, there may be a few images on the Internet I may prefer not to have come across, and there are certainly religious and superstitious ideas that I may prefer not to have been introduced into my head as a child... but again the irony meter is pegged, as it's precisely the people making the most noise about dangerous information that would instead prefer to fill children's heads with religious and superstitious ideas!
Many ideas have resulted in much trouble and suffering (Nazism, nationalism, communism, religion, etc.) However, I feel compelled to say, "Ideas don't kill people - people kill people."
If anyone would like to send me a link to the mythical "harmful information," I would be very grateful.