Daytime television has traditionally been aimed at children and housewives, who were the largest demographics expected to be home during the day. However, college kids, unemployed slackers, and other groups who are home during the day (or have access to a TV during daytime hours) have catapulted certain shows into mainstream appreciation.
Merchandise-DrivenTokusatsu is aimed squarely at kids. However, they cast a lot of pretty-boy actors to appeal to the mothers of the aforementioned kids, who often watch the show at home with their children. And if not the mothers, then it works well with the older sisters of these kids. And if the fathers stay around long enough to watch it at times, the actresses fill that niche nicely, along with the gravure to go with it. A second periphery demographic is the small but solid overseas fanbase, who tend to be in their late teens or mid-20s, overlapping somewhat with the Power Rangers fandom as well.
Spongebob and Fairly Oddparents are also longrunners, so it's also likely that young adults have grown up with these shows and still watch them.
The idea of the Sci-Fi Channel (or SyFy now) having a mostly young male demographic is increasingly fallacious, which the execs seem to have some difficulty recognizing; when confronted with the fact that many of their viewers are women, David Howe acknowledged that "almost half of our audience is women, thanks to shows such as Ghost Hunters that attract more women than men", completely ignoring the fact that many of their scripted shows (Farscape, The Invisible Man, the various Stargates, Battlestar Galactica (Reimagined), etc.) had/have significant (if not overwhelmingly, or at least more involved in online fandom) female audiences.
Kika, a German kid channel, has a mascot called Bernd das Brot (Bernd the Bread). The pessimistic bread became a cult favorite with young adults and teens in Germany. Kika started airing a looped program with Bernd instead of static after 9 P.M, attracting many insomniac young viewers.
Likewise with queer characters in Soap Operas, in terms of attracting LGBT viewers who normally don't watch them. The After Elton website, has a section dedicated to shows like this called "Gays Of Our Lives".
Soap Operas tend to be aimed at middle aged women. But they become quite popular among college students. The joke is that the televisions in student houses don't get many channels so the students end up watching soaps all day.
America's Next Top Model as well as any of the other Top Model shows have enough Fetish Fuel and Fanservice to attract male viewers.
Project Runway to a much lesser degree for similar reasons.
The Price Is Right was obviously designed to appeal to housewives, who would do most of the shopping for household items. Over the show's long history, however, it has garnered interest from just about every viewer demographic.
Bob Barker noted that the show got a lot of college fans after he was featured in Happy Gilmore and beat up Adam Sandler.
Wheel of Fortune and Jeopardy! likewise grew from mostly housewife appeal to pretty much universal. Especially since the mid-90s or so, they've taken to having more college-age students.
In England, Deal or No Deal is the show of choice, possibly due to the presenter (Noel Edmonds) having presented 90's show Noel's House Party. Probably more down to the fact that he's able to make a show about someone opening boxes seem quite tense and nail-biting. Even when all the big prizes have gone.
The Food Network's initial run of Iron Chef carried advertisements generally aimed at over-40-housewives, who were Food Network's primary demographic at the time. When the show was adopted by younger viewers due to its competition aspect and the Narm Charm of its presentation, Food Network was caught flat-footed and took a lengthy period of time to properly capitalise on the show's success by making it a centerpiece of their lineup. Rapid Network Decay soon followed.
Anthony Bourdain's first show was also adopted by a younger demographic than originally intended.
Teletubbies is a show aimed at extremely young children, but it became famous for attracting the attention of college/uni students and druggies, all of whom were often watching television in the middle of the day. The show's baffling and surreal nature, combined with its bright colors and hypnotically repetitive nature, made the show enjoyable with the right amount of irony or chemistry.
In the Night Garden is arguably even more cutesy, surreal and coy than Teletubbies, and makes perfect hangover viewing, or if you are so inclined, watching it stoned or tranquillised is amazing.
Speaking of Doctor Who that show itself probably belongs here; it was originally intended as a show that would teach history to kids, but when it started going more overtly science fiction (in its second serial no less) it started to bring in a lot more adult fans who would watch with their children, not to mention the kids who grew up and yet stayed with the show into adulthood thanks to its Long Runner status. It's a matter of (at times quite heated and interminable) debate, however, whether the show is a 'family' show (i.e. intended for both kids and adults from the start), a kid's show that happens to claim a strong Periphery Demographic among adults, a kid's show which eventually became a family show or something else entirely.
Although Beakman's World was generally aimed at 9-to-14 year old school kids, high schoolers and college students liked it too. Maybe it was because they finally got what they couldn't get in middle school; maybe it was because the main character looked like someone who'd do drugs; maybe it was the assistants (no, not the rat); or even a combination of all three.
Similarly, Bill Nye the Science Guy still has a significant following among young men, which may have been a factor in creating a similar series more directly targeted at them.
The Nostalgia Filter probably has a lot to do with this, since both these guys have been around since at least the early '90s. Who knows, it might even appeal to middle-aged/elderly Baby Boomers who remember Mr. Wizard.
In Seattle (where the show was filmed), a large part of the audience were older adults who really missed Almost Live, where the Science Guy and the other cast members got their start.
The children's TV show LazyTown is also known to be popular with teenagers and young adults as well as parents. At least some of this is due to entirely unwholesome reasons, though given Sportacus's and Robbie's tight pants we can be reasonably sure that some of the adult appeal is deliberate.
iCarly started off aimed at roughly the 8-14 market, but ended up being a massive hit in all the children and teen demographics (from young kids to mid teens). Since people caught on to the massive amounts of Getting Crap Past the Radar included, it's now a big hit with adults and college viewers as well.
Many parents and adults tend to view Yo Gabba Gabba as a Guilty Pleasure, although some of its appeal is from the show's baffling ability to somehow convince popular indie rock bands like Low, Mates of State, Hot Hot Heat, The Shins and Of Montreal to appear as musical guests.
It helps that the show was produced by a member of the Aquabats.
A growing number of Western fans in their 20-30s grew up watching Power Rangers. The fact that they brought back Jason David Frank (as a regular cast member for season 12) and Johnny Yong Bosch (in a guest spot for the 15th anniversary) would suggest that the producers are well aware of the older Power Ranger fans.
The 20th Anniversary series Power Rangers Megaforce looks to be catering to this demographic a bit as well as it will feature appearances from past Rangers possibly including Jason David Frank.
The Canadian TV series Trailer Park Boys is very popular with both criminals and police officers. The former are able to identify with the main characters (the producers even describe the show as "Cops from the criminal's point of view"), while the cops enjoy seeing depictions of what they have to deal with in their jobs.
It's also popular with both the lower-class demographic it depicts and more well-to-do people who find the portrayal of their lifestyle hilarious.
Word on the street has it that the live-action The Dresden Files TV series was cancelled because, while it had an active fan following, said fan following was mostly older women who didn't mesh with the rest of The Sci-Fi Channel's young male demographic.
As for Sci-fi examples, Stargate Atlantis was cancelled to make way for Stargate Universe so TPTB could appeal to a younger male demographic instead of SGA's (very large) female fanbase.
Considering the copious amount of almost soap-operish melodrama (at least in the opening episodes), it seems that SyFy have decided to try for Multiple Demographic Appeal with the show.
TPTB claim that the cancellation of SGA and the launch of SGU weren't direct causation. They have not convinced many fans that this is true.
The Vision Ongallery theme tune, so iconic it penetrated a national consciousness, can only be intended for the periphery demographic, as the intended audience was deaf children.
Sesame Street intentionally invoked this trope, in order to create a show that kids and parents would watch and enjoy together. This kids show grew its following gradually; when the original kid viewers grew up to be adults, they would subsequently watch the show with their own children.
Choujinki Metalder, the sixth Metal Heroes show, attracted a primarily older fanbase instead of its intended young audience due to its dark and complex storyline compare to previous Metal Hero shows. As a result, it was canceled at the end of its third course, with only 39 episodes instead of the usual 50.
Top Gear is a Petrolhead Show, but there are plenty of people who watch it without knowing much about cars, simply cause it is that hilarious, and it doesn't hurt that the film crew is great at making everything look good.
Both the producers and the star, Jeremy Brett, were surprised to learn that their 1984-1994 Sherlock Holmes TV series adaptation was very popular with kids, who seemed to see the lead character as a Super Hero. As such, Brett got permission from the granddaughter of Arthur Conan Doyle to have Holmes beat his cocaine addiction and bury his needle.
It's a little hard to find The Golden Girls' original demographic. Even during its debut it was very popular with younger demographics (and still is). When asked why, I think Betty White said it best, "Because it's funny!"
War miniseries like Band of Brothers and The Pacific, in theory and according to mainstream media, are generally geared at middle-aged-to-older men (Seth Meyers, making fun of Eric Massa, accused of groping a staffer at his fiftieth birthday party: "That's not what happens on 50th birthdays. On my dad's 50th birthday, we got him a gift certificate to Morton's and a Band of Brothers DVD"), including those who possibly served. However, they tend to have very strong fanbases of young women in their teens and twenties, partially because of the wealth of young men in uniform and the many shipping possibilities. However, many seem to have genuine interest in the history as well
Not to mention that said earworms are often played in teenage/adult clubs in Belgium.
The British teen drama Skins has multigenerational appeal thanks to its excellent writing and acting. In fact, adult fans probably outnumber teen fans outside of Britain.
It's no secret that the DCLAU's primary fanbase is made up of older teens and young adults.
Wishbone was aimed towards kids seven to fourteen, but it gained a lot of popularity from teenagers and adults, as well as many literature fans.
Horrible Histories, the live-action adaptation of the classic kiddies' history series, airs on the British equivalent of PBS Kids and is theoretically aimed at 6 to 12-year-olds... which in practice hasn't stopped the show's writers and performers from slyly directing it squarely at older teens/adults, who've responded in droves.
MTV's Teen Wolf has attracted a not insignificant adult gay following. Considering how much time the many attractive guys on the show spend shirtless, and the shows casual inclusion of a gay character and gay themes into some of its episodes, this may not be entirely unintentional.
The CBC has a significant American audience, thanks to the Canadian population living for the most part near the U.S. border. CBC stations can be picked up over the air in most cities bordering Canada, and the CBC is even carried on some cable systems in markets near the Canadian border.
Even though the humor of the shows would likely go well over kids' heads, it's not too uncommon to see late elementary school/early middle school age kids watch Seinfeld or Married... with Children reruns.
Dexter has an enormous female fanbase, probably because most women find his "damaged yet very mysterious" nature charming.
The Big Bang Theory is one of the most oddest examples of this trope. Even though most of the characters in the show work in a university, and it features a lot of nerd and geek references, it was always aimed at Adults 18-49 like many sitcoms of it's kind. However, since then, the show has accumulated a huge following with nerds and geeks, who not only appreciate the many science fiction and comic book/superhero references, but also can relate to many experinces the characters often go through. It's become up to the point where it's so huge, that the show itself has become apart of the nerd and geek entertainment.