What Do You Mean Its Not For Kids: Western Animation
One of the most controversial case of this trope (in the days before Seth MacFarlane's shows, but right around the time that The Simpsons was still popular) is when Beavis and Butt-Head (a pair of idiotic teenagers who do dangerous things and try to get laid) caught controversy for driving younger, more impressionable viewers into imitating their dangerous stunts (mostly setting things on fire and dropping bowling balls from bridges). When news of a boy burning down his trailer and killing his sister cropped up, the boy's mother protested the show's content (even though the family didn't have cable at the time of the incident). As a result, Beavis could no longer display pyromaniac tendencies or grunt, "Fire! Fire!" (though the movie and the revived series brought those back), most of the older episodes had to be edited to remove anything considered imitable, and the show was put on temporary hiatus and replaced with The Brothers Grunt, which is considered one of the worst shows MTV has ever aired (besides most of their current programming, of course).
The Seth MacFarlane cartoon franchise is the most frequent targets of the claim, including The Cleveland Show, American Dad! and most notably, Family Guy. Critics, including the Parents Television Council – in harshly criticizing the frequent very adult plots, extreme violence, crude language and lewd sexual situations – cite the fact that the show is animated, have child-friendly businesses (such as Burger King) as frequent advertisers, have merchandise marketed to children and its airing during early evening hours when children are potentially in the audience. Those defending the show often point out that the show's intended audience is not children and that some won't allow their children to see it, but those claims have often been refuted by the PTC and others. Even more so if one buys the DVD release. Some adult cartoons, like The Simpsons, are written to comply with broadcast standards, so what you see on television is (with few exceptions. The DVD versions of "Marge Gets a Job," "New Kids on the Blecch," "Viva Ned Flanders," and "Sunday, Cruddy Sunday" edited out Mrs. Krabappel's line about Bart feigning Tourette Syndrome, Mr. Burns calling Smithers a "Chinaman," Homer figuring out that Barney's birthday is on the same day as Hitler's, and a sexy Superbowl commercial about The Catholic Church respectively) what you'll get on the DVD. The MacFarlane cartoons are written first and then censored for broadcast, so the DVD versions are often more explicit.
One of the biggest is South Park; despite airing at a time when kids should be in bed, some watch it anyway. Despite the animation using a paper cut-out doll style, it is full of swearing, violent death, gore (especially in the later seasons), uncensored cartoon nudity, implied sexual abuse and rape, and child abuse both implied and confirmed. People with various prejudices aren't always directly punished, and childish innocence is rarely a good thing, which might confuse children. It also makes fun of Political Correctness Gone Mad, references many current events, and features a manipulative, sociopathic, anti-Semitic little boy (Cartman) as one of the show's most popular characters. It also doesn't help that from seasons one to six, the theme song was more cheerful and unassuming, which lured a lot of people into thinking it wasn't that bad (yeah, never mind the TV-MA rating and that warning that says all the celebrities are impersonated and the show's content is so vulgar that nobody should watch it)
You'd think sixteen years later, this wouldn't happen much anymore. Well, it still does — at least when it had that short-lived syndicated run on free-to-air TV. The FCC received complaints of kids overhearing the show or trying to stay up late to see it, and it was subsequently canceled (which is why King of the Hill and Futurama now rerun in syndication and why Comedy Central airs the the syndicated episodes on their channel).
The Simpsons has dealt with adult subjects like animal abuse, child abuse, politics, alcoholism, religion, class inequality, and juvenile delinquency, but back when it first aired, a lot of people didn't accept it as an adult cartoon because of how simplistic the animation and art was, and trashed it for corrupting youth due to the subject matter and having Bart Simpson (who, back then, was written as a more destructive, 1990s spin on Dennis the Menace) as the main focus of the stories. It also didn't help that Simpsons merchandise back then were sold as children's toys.
The Simpsons was even, in 1991, declared by Channel 4 to be the Greatest Kids' TV Show ever, despite not actually being a kids' show.
Word of God says it was never meant to be a kids' show and the bright color scheme was meant as an attention-grabber for FOX executives and viewers who just happened to be channel surfing.
Teletoon, the Canadian version of Cartoon Network, specifically airs warnings before and during each show from 9pm on (the "Teletoon at Night" block) that the shows are not intended for children. They actually build in a margin for error in that they start with an hour of Futurama and then come the shows like Moral Orel, Archer, and Squidbillies. By the time the later shows roll around, the warnings include comments like "...meant for 14 years of age and older. And if you aren't 14, what are you doing up this late?"
Slacker Cats. It was on ABC Family. The first episode alone has necrophilia. And pornography. As for why it was on ABC Family? The original sale from the Christian Broadcasting Network to Fox/Saban contained a stipulation that the channel contain the word "Family" in the name forever, no matter who owns the network. And no matter what's actually on the channel, apparently.
Looney Tunes (the original shorts from 1930 to 1969) have, according to its directors and how it was distributed back then, been meant for general audiences (i.e., kids and adults, though most of the humor in the Looney Tunes cartoons would either be too risque for kids or wouldn't be readily understood by kids). When the cartoons were syndicated for TV, a lot of the cartoons had to be edited or banned outright so it can appeal to kids (and a new generation of adults who would see some of the outdated jokes and scenes as racist, sexist, or un-PC). The DVD releases of the cartoons have the shorts uncut and even include a warning in the beginning, stating that the cartoons are products of a different era and should be seen from a historical perspective.
The Flintstones, when the Hanna-Barbera production company launched for television in 1957, they intended to gear their cartoons for children. However, some of the shows (The Huckleberry Hound Show, especially) proved so popular with adult viewers that the networks began airing them closer and closer to prime time; this inspired Hanna-Barbera to develop a show specifically for prime time, which of course turned out to be The Flintstones. Even then, the cartoons were considered "family shows" in the most literal sense of the word: programs that would appeal to kids and adults equally.
Similar to the above is Wait Till Your Father Gets Home. It's a Hanna-Barbera production from the late 1960s and often released on Cartoon Network and Boomerang so people get the impression it's for children. However it's more like a 1970s version of King of the Hill (only Harry isn't as uptight as Hank Hill, but he thinks Chet has failed him as a sonnote like Hank with Bobby, only it's because Chet dropped out of college, not because he isn't interested in sports and manly activities and is uneasy about sexual mattersnote especially when it comes to Alice trying to be sexually liberated, as seen in "Alice's Dress", Irma comes off as Peggy Hill in the early episodes: sane and a bit dull, but does have dreams of being more than just a wife and mother, and Harry's neighbor, Ralph, isn't as insane as Dale, but he is that kind of hyper vigilante who thinks America is falling apart due to sociopolitical change) mixed in with a watered-down All in the Family.
Similar to The Muppet Show example in Live-Action TV, the first Shrek movie was meant to feel slightly more like a movie for adults than for children, and contained mild language and more innuendos than its sequels. As one result of this, the movie's toys were made by Todd McFarlane's company (specializing in detailed, collector-grade action figures) - hard to believe for some, given the more "toyetic" and child-oriented merchandise of the sequels.
Fish Police was a Hanna-Barbera cartoon about anthropomorphic fish, with colorful backgrounds and many fish-themed puns, very loosely based on the comic book series and aired as an early competitor to The Simpsons (back during its Golden Age when it was seen as the greatest American television show, and not a lesson on why most TV shows should just quit if they start to run out of steam). It was also filled with content that went beyond what can acceptably be considered Parental Bonus in a "kids'" cartoon — including an episode that had an underwater version of a red light district (a part of an urban neighborhood filled with legal and illegal sex businesses, such as sex toy stores, X-rated video stores, strip clubs, and, of course, pimps and whores on the street).
Duckman: It's about a cartoon duck, and it's made by the nice people who brought us Rugrats. If only it weren't for the language and sex-related jokes.
Stressed Eric also qualifies (although Klasky-Csupo didn't animate season 2). There's an ENTIRE EPISODE about sex. But that didn't stop many young kids from watching the show...and subsequently getting terrified by the end of every episode, where Eric's stress vain strangles and kills him.
The animated shorts collection Batman Gotham Knight features horrific violence - and unlike the live-action version, it isn't bloodless. The usually more conscientious commonsensemedia.org thinks Gotham Knight is appropriate for 11-year-old children (in comparison, they unanimously thought otherwise for The Dark Knight). Because it's animated, and it's about Batman, right? Thank God none of the shorts featured The Joker, there would be kids in therapy. Some stores even sell the film in the children's section, and it was even aired on Cartoon Network. No, not [adult swim], regular daytime Cartoon Network, albeit with a TV-14 rating and some of the violence toned down.
Batman: Year One and Batman: The Dark Knight Returns are rated PG-13. They earned those ratings... prostitution, violence, hard edged vigilantism, and Anti-Hero-ism are the norm, with The Dark Knight Returns having both a Nazi transvestite with swastika pasties making the cut, as well as the gruesome massacre and death of The Joker. Not only does DC Showcase: Catwoman have graphic portrayals of strippers, but Catwoman takes part herself.
All three movies mentioned above are part of the line of DC Universe Animated Original Movies, all of which are aimed more towards adults and teenagers than younger kids (the fact that they're rated PG-13 should point this out, though some movies aren't as dark as others) and could count for this trope. The biggest case would be Justice League: The Flashpoint Paradox, which contains very disturbing and Squick-inducing content that manages to surpass The Dark Knight Returns.
Bromwell High. Despite being barely well-known, it is probably the most triumphant example of this trope. It airs on the Canadian kids network Teletoon, so that means it automatically is for kids, right? WRONG! You can never go through an episode WITHOUT major uses of the F and S words, and it features a LOT of sexual references (and Latin American tropers, it also aired on [adult swim] for a reason) yet it got a DVD release by the FAMILY division kaBOOM! Entertainment and airs on the Australian children's network ABC 3. Naturally, the DVD release got a CHVRS rating of 18A (the equivalent of a US R rating).
Brickleberry. At first glance, someone may think it's perfectly fine for kids since the animation and art looks like something from a Saturday morning show in the 1990s and it has talking animals. It's...not. If the cold opening of the first episode (where Steve shows a bunch of horrified Boy Scouts a meadow filled with animals having sex) doesn't make you believe, then look up all the reviews (most of which are negative) about how this show is an excessively vulgar clone of Family Guy and South Park, with none of the self-aware goofiness or scathing satire of either show.
According to Todd McFarlane, when he first started pitching an animated version of Spawn, the networks he talked to wanted to make a Saturday morning version. Right down to talking animal sidekick, though at that point he may have been being sarcastic in his recollections. It seemed none of the big-wigs realized that a character whose name was short for "Hellspawn" and who was horribly burnt head to toe and fought against multiple angels and devils across Earth, heaven and hell itself wasn't a good fit alongside the light-hearted fair common to those slots. Then again, when he finally got the nod from HBO, airing past-prime-time with numerous warnings of its content, people still complained that this 'kiddie cartoon' was so graphically violent and sexual, leaving him feeling like he never should have bothered in the first place.
Young Justice. You're telling me the concept of a covert team of vigilante child soldiers fighting a super villain Illuminati while slowly but surely crossing whatever lines they have to (up to and including faking the death of one of their own by another member so she might be planted as a deep cover agent in said organization) slowly being torn apart on a psychological level by all their secrets is supposed to be an innocent adventure in the DC universe? Also, the whole show had pacing that was much more deliberative than most children would be used to. Given its time slot, god only knows who it actually was for.