nearly one in 10 12-13 year olds were worried they were addicted
I would say this is more likely to be a problem with their social / religious upbringing making them think that it's messed up to want to look at porn more than a couple times per week.
Without knowing more about their definition of "addicted" we can't be sure, but introspection is socially accepted for things like "being offended" and whatnot, so I see no reason not to take their concern at face value.
Also, feel free to make as many kid-friendly whitelists as you want but proposals to rate/blacklist the entire thing are horribly insidious. Why are we still falling for this old scam? In addition to being insanely hard to do effectively, this sort of censorship is ALWAYS stealthily aimed at adults, not children. Case in point: NC-17 ratings for movies and AO ratings for videogames. Both are on their face completely redundant (R rating and M+ rating), but their real use is to prevent certain content from being produced through self-censorship pressure by retailers/theaters refusing to carry the highest rating.
No, they're not redundant. R/M+ are intended for adults, and children with parental consent. NC-17/AO are intended for adults only and not children, even with parental consent. It's not legally enforceable in most jurisdictions, but bowing to public pressure most mainstream cinemas will enforce as a matter of corporate policy the relevant age restrictions. In the US, "NC-17" was specifically created to allow it to be used for movies that warranted the restriction but weren't "pornography" in the sense associated with the previous rating, "X".
The main reason more "mainstream" movies don't come out as NC-17 is simple... They're likely to make more money the more people are easily able to see them. Frankly, this is why a fair number of movies try to end up as a strong PG-13 instead of an R rating -- bigger audience, and less worry for the parents about having to decide whether they really want their kid seeing the film before they accompany them.
Ironically, it goes the other way for 'G' films. Especially nowadays (morals and community standards change over time, naturally), there are plenty of films that could and would be rated 'G', but unless you're making an animated feature it's considered something that will keep the audiences away (what teen wants to see something G rated?). Often studios and producers will put some sort of slightly-unnecessary smack or violence, or a mild curse, or something exceedingly brief *just* to nudge a film up into the PG category, so it brings in more revenue.
Goes both ways.