• Sunday, November 10 marks the 50th anniversary of "Sesame Street."
• There have been countless tender and wholesome moments in the show's history, but it's also been criticized at times for covering difficult issues and unintentionally offending audiences. 
• Here are 11 of the most controversial moments in the show's history. 
• Visit Business Insider's homepage for more stories.

The beloved children's show "Sesame Street" will be celebrating its 50th anniversary on November 10. And with half a century of airtime under its belt, the show has provided important childhood lessons for millions of people.

But it hasn't always been "sunny days" for the puppet-driven series. 

While the long-running show is known for its wholesome content, it isn't without its controversial moments. From introducing characters who address polarizing real-world issues to tackling serious topics like death and grief, "Sesame Street" has faced its fair share of criticism. 

In honor of the show's half-century-long history, here are 11 of the most controversial moments in "Sesame Street" history.

'Sesame Street' debuted in 1969, and cultural attitudes were so different back then, that when old episodes were released in 2007, they came with an 'adults only' warning.

Despite its reputation as the children's show we all know and love today, the early seasons of "Sesame Street" might not pass muster in today's TV landscape.

When the show first aired in 1969, it featured a number of scenes that adults of today might not feel comfortable showing their children. In some episodes, children played in construction sites and jumped on old box springs; in others, Cookie Monster was shown smoking a pipe.

When episodes from this era were released on DVD in 2007, they came with an "adults only" warning.

"These early Sesame Street episodes are intended for grownups and may not suit the needs of today's preschool child," the warning read, according to The New York Times.

Roosevelt Franklin, the first black Muppet on 'Sesame Street,' was accused of perpetuating negative stereotypes about black children and was removed from the show in 1975.

Roosevelt Franklin was a main character on "Sesame Street" from 1970 to 1975, and was the first black Muppet to appear on the show. Franklin was later removed from "Sesame Street" after parents criticized the character for promoting a harmful stereotype that black children were "rowdy" and a "bad influence" to other children. 

While Roosevelt also taught lessons on African culture and geography during episodes, his bad behavior and regular visits to after-school detention ultimately catalyzed his departure in 1975.

Snuffleupagus was a figment of Big Bird's imagination until 1985. He was revealed to the rest of the cast as real after criticism that the other characters not believing Big Bird would silence childhood victims of sexual abuse.

Mr. Aloysius Snuffleupagus was introduced to 'Sesame Street' in 1971 as an imaginary companion to Big Bird. While Big Bird discussed his large furry friend with other characters on the show and even insisted he was real, none of them believed Snuffleupagus was anything beyond a figment of Big Bird's imagination.

This continued for 14 years until adult viewers complained that a failure to accept Big Bird's reality, despite his firm belief that Snuffleupagus was real, could send the wrong message to young audiences.

With numerous cases of childhood sexual assault making headlines around that time, show executives did not want to convey to their young audiences that adults may not believe what they say. 

"All this was really stemming from a specific set of incidences in the news, claims of sexual abuse going on in some daycare centers, and kids being questioned about what was going on," Carol-Lynn Parente, executive producer for Sesame Street, told Mental Floss in 2015. "The fear was that if we represented adults not believing what kids said, they might not be motivated to tell the truth." 

Snuffleupagus finally appeared as a character for all cast members to see in 1985. In the scene, cast member Bob McGrath remarked to Big Bird, "From now on, we'll believe you whenever you tell us something."

When the actor who played Mr. Hooper died in real life, the show wrote the character's death into an episode.

When well-known "Sesame Street" actor Will Lee died of a heart attack in 1982, it presented a challenge for the show's writers. Rather than writing a different reason for Lee's character, store clerk Mr. Hooper, to leave the neighborhood, the writers decided to confront the issue of grief head-on and make it a learning experience for their young audiences. 

A tribute episode titled "Farewell Mr. Hooper" aired in November 1983. The episode depicted Big Bird asking a group of adults on the show were Mr. Hooper was, followed by the tearful grown-ups explaining that Mr. Hooper died to a crestfallen Big Bird.

"Mr. Hooper's death was revolutionary because of its frank discussion of a complicated subject that does not fit squarely into the box of children's entertainment," Molly Eichel wrote for The AV Club.

Kami was introduced as the first ever HIV-positive Muppet on the South African version of 'Sesame Street' in 2002.

In 2002, the South African version of "Sesame Street," "Takalani Sesame," introduced the franchise's first HIV-positive Muppet, 5-year-old girl Kami, in an effort to address the HIV/AIDS crisis in South Africa.

Because many children in South Africa were being affected by the disease at the time of her creation, Kami served to educate a young audience about living with the condition. President Bill Clinton even appeared in a PSA with the character.

Due to heightened concern about the growing rates of childhood obesity in the US, Cookie Monster got a healthier diet in 2005.

Cookie Monster has been a main character on "Sesame Street" since 1971. But in 2005, parental concern over the rise of childhood obesity prompted writers to introduce more fruits and vegetables into the Muppet's diet.

The show began working in lessons like "a cookie is a sometimes food" rather than a consistent snack, while fruit is an "anytime food."

The change prompted fears among adults that the beloved character was abandoning cookies altogether, was changing its name to "Veggie Monster," or worse, was getting written off the show entirely.

Cookie Monster himself took to Twitter to clarify the situation: "Time to put end to rumors," the Muppet tweeted in 2010. "YES, me eat vegetables. NO, not going to be called Vegetable Monster! Dis whole thing silly."

The Israeli version of Sesame Street introduced Mahboub, an Arab-Israeli Muppet who spoke Hebrew and Arabic, as a response to the growing Israeli-Palestinian conflict.

The Israeli production of "Sesame Street," "Rechov Sumsum," introduced a Muppet named Mahboub in 2006. Mahboub is an Arab-Israeli Muppet who is bilingual in Hebrew and Arabic, and was added to the show in an effort to promote tolerance to the show's young viewers. 

The character's introduction came as a response to the growing Israeli-Palestinian conflict, a thorny issue for a children's show to tackle.

"Children today growing up in Israel are living in a very tense time," Alona Apt, the producer of "Rechov Sumsum," told the Jewish Telegraphic Agency. "They are affected at a very early age in terms of their aggressiveness to each other. The main goal is to show a different kind of reality, a different kind of street, to show children what common life can look like."

In 2009, Oscar the Grouch raised some eyebrows after taking shots at cable news stations CNN and Fox News.

The writers of "Sesame Street" were accused of making fun of Fox News in a skit featuring Oscar the Grouch in 2009. In the episode, Oscar appeared as an anchor on the Grouchy News Network, GNN. During his segment, the Muppet receives a call from a viewer who says "From now on I am watching Pox News. Now there is a trashy news show." 

A PBS representative responded to a complaint from Fox, stating that although the skit was "too good to resist, it should have been resisted."

Katy Perry's guest appearance was pulled in 2010 after parents complained that the pop star's wardrobe was too revealing for young audiences.

"Sesame Street" announced that it would not be airing a musical performance featuring Elmo and pop star Katy Perry in 2010 after receiving a number of complaints from parents that the singer's outfit was too revealing for the show. 

The show's executives released a statement: "In light of the feedback we've received on the Katy Perry music video, which was released on YouTube only, we have decided we will not air the segment on the television broadcast of 'Sesame Street,' which is aimed at preschoolers."

Perry's responded to the controversy on Twitter, saying, "Wow, looks like my play date with Elmo has been cut short!"

The 'Sesame Street' YouTube channel was hacked and replaced with porn in 2011.

Online viewers and show executives alike were shocked to find that on October 16, 2011, the YouTube page of "Sesame Street" had been hacked, with all of its videos replaced with pornography. The videos were quickly removed, but likely not before some of the channel's 148,000 subscribers got an unexpected lesson.

The nature of Bert and Ernie's relationship has always been in question, and for some viewers, whether they're roommates or romantic partners is still unclear.

The nature of Bert and Ernie's relationship has long been the source of speculation. In 1993, the show attempted to clarify the famous pair's dynamic by stating that they were roommates, friends, and nothing more — they do not portray a gay couple.

The statement did little to quell people's imaginations, though. A mockumentary about the duo's relationship was released in 2002, but it had had barely been screened before audiences before the filmmaker was hit by cease and desist letter.

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