Interestingly, as much as Darker and Edgier is considered a good thing, it is quite lighter than the mainstream comics. It turns out that if you tell a good story, people will enjoy it over a poor one that has more blood and swearing.
The Boom Kids comics based on the old Disney Afternoon shows. Nothing outright offensive about the material, but, due to massive Continuity Porn, they'll only make total sense to people who've seen the shows — which Disney has barely aired at all in the past decade and not at all since 2006. If you're under 20, chances are you'll be confused from Issue One. Oh, and they also cost a dollar more than most comics.
To its credit, Boom Studios seems to have realized this. The worst offender, Darkwing Duck, no longer has "Boom Kids" anywhere on the cover (though it's likely still placed on the kids rack at comic book stores).
Though, it should be noted that in many European countries, especially the Netherlands, Disney comics are so universally popular that the comics made just for those regions really aren't for kids anymore.
EC Comics. The entire company output qualifies, even after correcting for Values Dissonance for their being published in the 1950s. Even back then, however, Moral Guardians raised plenty of objections that their comic books were inappropriate for kids; EC strenuously resisted censorship until the Comics Code went into effect.
This trope was invoked in a Bloom County strip, where one character is going around telling everyone "the awful truth" about, well, everything. He comes to Steve, and says "The truth is, Knight Rider is a kid's show!" to which Steve replies. "Can't be. Can't &%^#ing be!"
Little Nemo. It's a whole nightmare world! Though this is more of a shift in what is acceptable for children. It was a lot more open at that time as shown with other so-called children's books during that time like The Wind in the Willows, which would almost be impossible to publish as a kid's book now. There's even a panel where Little Nemo, who is about nine at that point, is reading Gulliver's Travels.
Depending on the incarnation, Starlight Express includes hate-motivated beatings, a Serial Killer villain, Domestic Abuse, marital infidelity, a young woman singing a solo about her favorite sexual experience, a retired prostitute, a character who maintains an equal-opportunity harem, an ocean's worth of sexual innuendo in general, and references to smoking, alcohol, and drugs. The show manages to get away with all these elements because the characters are anthropomorphic toy trains. The Las Vegas version of the musical, which featured the main female characters in showgirl costumes, actually wasn't intended for kids, but attracted family audiences regardless.
In the 2011 Dance Off With the Star Wars Stars, which is for children, Darth Vader performs C. Lo Green's "F**k You!" (or at least the radio edit) during the freestyle half of the show.
Transformers. There are fans who insist that Hasbro and Takara should only make big, expensive toys for the adult collector market and ignore those little kids who buy the toys to play with. Some have actually complained about Transformers Animated because it has humor and plots aimed at pre-teen kids, which are the Target Audience of almost all Transformers incarnations.
Hasbro actually tried a line of big, expensive toys for the adult collector, and it didn't sell well enough to keep it going for too long. Turns out the adult collectors are a smaller pieceof the pie than they thought, and kids are in fact the primary consumers of toys. Who knew?
It should be noted just how much of Simon Furman's work fits into this category. When the writer of the bloodbath the Marvel Generation 2 comics became calls something too dark, you know you've taken Darker and EdgierUp to Eleven.
Furman was specifically concerned about the "For Kids" part of this trope. He was very much about darker, more fatal Transformer stories, but he was explicitly writing with an older audience in mind than the cartoon series are marketed towards.
It's a bit understandable, though, if you look at the premise devoid of context: Two factions of a race of alien war machines come to Earth, their war having gone on so long that battling for the resources our planet can give them to continue the war effort is more important than the war itself. The weakest of them has enough power to slaughter dozens of human soldiers and come away with nothing more than a badly-scratched paint job. At best, their feelings towards us are paternalistic, and they look down with a combination of pity and admiration on those of our species who see it as their sworn duty to defend us from them. At worst, they find us repulsive and enjoy slaughtering us when they have a chance. A sunny kids' show is not what you'd imagine it would look like..
G.I. Joe as a whole gets this treatment, actually. Because it happened in the comics, there are those older viewers/readers who think that every TV show and movie—past, present, future, and otherwise—should use real bullets instead of (the Hasbro-mandated) lasers, and that there should be more onscreen deaths simply because of the military nature of the concept and toyline (which goes all the way back to the 1960s or 70s; i.e., before the "Real American Hero" era). Aside from the aforementioned Resolute, the closest the fans got to a version of Joe they wanted was probably the live-action movie. Nonetheless, it's still a family franchise, even if the fans think it should be otherwise.
LEGO. Have you ever met someone who has outgrown those silly little blocks?
The LEGO Group is a funny case though, as it is aware of its older fans and does things like adding Shout Outs to older series (such as Classic Space) or continuing series from the 1980s, like Space Police and Pirates. It also produces sets marketed at adult fans, starting with Cafe Corner; fans seem to be rather aware of the true target of their hobby (with exception of a few complaints over BIONICLE).
It is worth noting that LEGO bricks were originally sold as a tool for architects to create models of their future works with.
And now they're ending the BIONICLE line, because they think the story is too long for the younger kids to enjoy. Older fans are not pleased.
The adult fandom does not lack the occasional guy that complains about sets - specially colors or the lack of a realistic military theme - being too childish lately...
The properties they choose to adapt for the LEGO Adaptation Games and toys also skew towards PG-13 rated titles. Star Wars and Harry Potter are initially PG material (with the later, darker ones being PG-13) but we also have the Burton/Schumacher Batman films (all PG-13), the Pirates of the Caribbean films (likewise) and the Indiana Jones series (first two are PG, but only because PG-13 didn't exist, and Temple Of Doom was partially responsible for its creation).
While not a big deal back in the 1960s when they were made, post-modernism pretty much guarantees that these bad boys won't be seeing a revival: Meet the Ding-a-Lings!
For a short period of time, there were vibrating Harry Potter broomsticks in toystores. Which were enjoyed fondly by... well... all ages, until it was brought to the companies attention that not everyone was riding the broom pretending to play Quidditch...
Technically any webcomic ever could be this, since there are laws about letting anyone under 13 years old use the Internet unless supervised by a parent or guardian.
Sonichu is nominally intended to be a children's comic, aimed for kids between the ages of 7 and 14...but that certainly doesn't stop its author from inserting scenes of bloody, brutal violence (up to and including a scene of a young girl mutilating a defenseless criminal with a pair of giant drills) and (supposedly) titillating sex (with an entire chapter dedicated to showing off the main characters' sexual anatomy). Needless to say, no children even read the comic in the first place.
The creator of Liltoon once had an on-site notice stating that his comic is suitable for readers aged 10 and up, but the recent "Flushing the Soul" arc seems to belie that.
Neopets is a rather weird example in itself; nowadays the target demographic audience is definitely for young children- but when this popular site first started out, it was mostly used by college (or university) students years ago. There are still remnants of this material from that time (such as the Ski-Lodge Mystery plot) floating around, waiting to be prime scariness for any children who happened to stumble across them.
The creator of the fanon SpongeBob spinoff Warriors of Bikini Bottom claims the show is intended for middle school age and up, but that doesn't stop it from having characters discussing their sex lives (and on occasion, even having sex), swearing in the transcripts, and having various gory fights.
Doctor Steel's whole concept for "The Dr. Steel Show" was that of a kid's show that was just a little bit... warped. He also had a song, supposedly for a proposed kid's show, called "Smokey the Kid-Loving Trout" (graphic for this song on his website showed a stinking hobo-like anthropomorphic trout, complete with stogie, walking with children).
Bubblegum/candy cigarettes — and also, licorice pipes, chocolate cigars, candy cigarettes, and the infamous "Hippy Sippy". Aside from the last item, these are still sold today (although often with bowdlerised names like "candy sticks"). Even a few of the most ardent anti-smokers still feel a little pang of nostalgia for these, and feel kind of torn at the idea of taking them off the market.
People who don't come from the parts of the country where a large percentage of the population is of Mexican (or possibly other Latin American) descent might feel this way about the most popular confections for children in those regions. Chicano children go wild for sour and/or spicy treats such as sal limon (a sour citrus powder with salt), Chinese candy (bitter plums rolled in a sour powder), Lucas (a chili/sour citrus powder mixture either consumed by itself or sprinkled on top of fresh fruit), and whole sour dill pickles.