In his sermons, Martin Luther King Jr often made reference to his daughter Yolanda Denise seeing him off to the Atlanta airport before work trips and passing an amusement center called Funtown along the way. When she’d ask if he could take her some day, he’d always find a way to change the subject because he couldn’t bear telling her that she “couldn’t go to Funtown because of the color of her skin”.

When they were first built in the early 20th century, amusement parks were not intended for Black families. And while, 70 years on, King’s dream of seeing Black and white children play “as sisters and brothers” has mostly come true, the past week offered a stark reminder of the progress there still is to make.

On Wednesday a Black father accusing multiple characters at Sesame Place, “a children’s theme park celebrating Sesame Street”, of snubbing his five-year-old daughter during a meet-and greet filed a $25m lawsuit against the amusement park for “pervasive and appalling” racial discrimination.

The lawsuit, filed in a Philadelphia federal court, comes less than a week after a Brooklyn woman named Jodi Brown posted a nine-second video of her young daughter and niece being spurned by an employee in costume as the character Rosita. That clip, which is closing in on a million views, prompted other parents to share video proof of Rosita, Zoe and other characters at the park passing up their kids to hug and high-five with fairer-skinned children.

Amid public calls for a boycott of Sesame Place, the Congressional Black Caucus and NAACP have asked to meet with executives at the park’s parent company, Seaworld Parks and Entertainment. On Saturday, a few dozen protesters rallied for hours outside Sesame Place, which is located in the north-east Philadelphia suburb of Langhorne.

In the federal lawsuit, which seeks to become a class action, Quinton Burns of Maryland alleges that when he and his five-year-old daughter attended a Sesame Place meet-and-greet on Fathers’ Day, they were purposely ignored by four costumed performers playing Ernie, Elmo, Telly and Abby. On Wednesday, Burns released his own 29-second video of the characters passing over his daughter for a high five to interact with white children. “Just looking at her face, it makes me want to cry every time I see it,” Burns said at a courthouse news conference.

Sesame Workshop, which created the park’s characters and owns the licensing rights but does not own the park, has been quick to condemn the incidents and urged park executives to act swiftly.

It almost beggars belief that Sesame Street could be associated with a racial discrimination lawsuit. The children’s TV series was conceived amid the social justice movement of the 1960s as edutainment for -children from disadvantaged backgrounds and an inclusionary showcase for Black and Hispanic actors. The state of Mississippi banished the show from its airwaves in 1970 for having too diverse a cast. The character Rosita, who has been around since 1991, hails from Mexico and was Sesame Street’s first regularly appearing bilingual muppet, toggling between Spanish and English.

But the history of a radical and diverse TV show clashes with the story of amusement parks in America. The 1875 Civil Rights Act included a line mandating equal access to public accommodations, but the supreme court wound up undermining the latitude to enforce that law.

This meant that at the 1904 World’s Fair, which was held in St Louis in conjunction with a disastrous summer Olympics, put Black and brown bodies on display. A group of African pygmies branded savages were showcased in a hollow that had a walkway over the top so white visitors could point down and laugh. A year later one of the men in the exhibition, Otis Benga, was relegated to a Bronx Zoo display cage.

Amusement parks as we know them today, says Victoria Wolcott, a University of Buffalo history professor whose 2012 book Race, Riots, and Roller Coasters takes in the dark arc of public leisure space in the US, “emerged at the nadir of race relations”, as the country was segueing out of reconstruction into segregation. The parks were often marketed with dog whistles like “clean” or “safe”, and they stationed sentinels at their gates to enforce the whites-only policy. If a Black family did happen on to the grounds in these early days, they could expect to be beaten bloody for their mistake.

At Coney Island, park operators made games out of brutality. The park, like many in the US in the early 20th century, had an attraction called the African Dodger, in which white ticket holders would attempt to hit baseballs at the heads of actual Black people – a number of whom suffered broken noses, teeth and other serious injuries.

“This was not that long ago,” says Dewey Clayton, a University of Louisville political science professor who vividly remembers not being able to set foot inside the white section of a Myrtle Beach amusement park the same July day President Lyndon Johnson signed the 1964 Civil Right Act into law. “It was in my lifetime. Too many of my colleagues here at the university and in the area have had just really sad experiences like that as children.”

The exception among amusement parks was Disneyland, which didn’t discriminate among would-be customers as long as they could fork up the money for an entrance fee, which few other parks charged at that time. But while Black families were allowed at Disneyland, the cover charge and lack of public transportation to access the park meant it was out of reach for many.

The Congress of Racial Equality, which bolstered King’s non-violent activism, was formed largely in response to discrimination at theme parks and other recreational spaces. “One of the things that was really so sad was reading memoirs of African American activists who talked about that exclusion when they were children as being absolutely searing,” Wolcott says.

In 2013, a Black family from San Diego sued Disney for discrimination after their children were snubbed by an employee in costume as White Rabbit, the time-obsessed character from Alice in Wonderland. The case, actually titled Black v White, was quickly settled for an undisclosed sum. It could serve as precedent in what could be a landmark class-action suit against Sesame Place.

In a series of statements last week, Sesame Place issued “heartbroken” apologies to the affected families and vowed to institute mandatory bias training for employees. It has thus far declined to say if any employees had been disciplined.

Win or lose, Burns, the father who brought this legal action, hopes to send a clear message: “This is unacceptable,” he said at his news conference, “and we will not stand by and let this continue.”