People love ball pits. On March 1, The Beach Detroit, an “interactive installation” that’s really just a giant pool of white plastic balls, opened in a skyscraper in the city’s downtown. By March 2, the first two weeks of reservations were booked solid. Snarkitecture, the architectural collective behind this massive success, has been touring various iterations of The Beach since the project first debuted in 2015 at the National Building Museum in Washington, DC. Then as now, the art installation is equally popular for families with children as it is for childless adults.

Over the past several years, ball pits have made a huge comeback. They were a ubiquitous part of any indoor children’s playground in the 1980s and ’90s, and you can now find adults taking selfies in vast pools of colorful plastic balls at Instagram-friendly pop-up museums and bars, on boats, and even in offices in New York, Philadelphia, London, Sydney, Mexico City, and beyond. YouTube is replete with videos of people filling their living rooms with plastic balls — amusing themselves as well as their dogs. Zoos in Houston and Denver have made ball pits for their mongooses; the Indianapolis Zoo created one for its meerkats.

There’s something about swimming in a vat of colorful balls that people and animals of all ages find simply delightful. Of course, ball pits also make for fantastic social media fodder, a resurgence perfectly timed to the Instagram age.

The invention of the ball pit (or “ball crawl,” as it was first dubbed) is widely attributed to Eric McMillan. Born in England and an industrial designer by training, McMillan moved to Canada and worked as an exhibition designer for Expo ’67 in Montreal. In 1971, he was appointed chief designer of Ontario Place, an ambitious project that included a park, a theme park, and the world’s first IMAX theater on newly built artificial islands just off the Toronto waterfront. Ontario Place was a visionary project, but it was missing something.

“One of the ‘mistakes’ was the project’s lack of child appeal,” McMillan notes on his website. Striving for a more kid-friendly environment, the designer created the Children’s Village, a massive playground unlike any other, where youngsters could climb huge rope nets and soft pyramids, crawl through hanging tunnels, and jump on an enormous air mattress. “The Children’s Village opened in July 1972, and it was an amazing success,” McMillan writes. “People loved it, and it quickly became the top attraction at Ontario Place. Suddenly I became the world’s expert on child’s play.”

While Ontario Place launched McMillan’s serendipitous career in playground design, contrary to popular belief, it wasn’t the site of the very first ball pit (although it would house one later). According to McMillan, that honor belongs to the ball crawl he installed in 1976 at SeaWorld Captain Kids World in San Diego, another of a handful of theme parks McMillan designed — his most famous being Sesame Place on the outskirts of Philadelphia, which opened in 1980, complete with a giant ball pit called the Count’s Ball Room. (80,000 plastic balls … mwa ha ha ha ha.)

Due to his use of rubber, foam, vinyl, and plastic in playground designs, McMillan is often referred to as the “father of soft play.” As he told UPI in a 1975 interview, almost everything he built followed four priorities: economy, ease of maintenance, safety, and the child’s pleasure, in that order. Although McMillan prided himself on his ability to create playscapes that evoke a child’s sense of imaginative exploration, his priorities were rooted in practicality and safety.

“In the 1970s, we became really risk-averse,” says play historian Susan Solomon. “After World War II, there was a tremendous interest in unique, architect-designed playgrounds, but things changed when people became concerned about abduction.” It was around this time that play was moved indoors, where it’s safer, “at least psychologically,” Solomon adds.

Playgrounds in the US originated in the 19th century in urban areas as part of reform movements with a political agenda to get kids off the street. And they weren’t just for kids. “In the 1910s, outdoor playgrounds were as much for adults as for children, available at night for adults to work out,” Solomon says. But once the 1970s rolled around, parents were increasingly more cautious as to where and how they let their children play, leading to a rise in indoor play spaces (perfect for a giant pool of plastic balls, which would be entirely impractical outdoors), as well as a concept Solomon calls “KFC”: playgrounds created from uniform kits, often including a fence and carpet. “These became cages for kids, and very limiting,” she says.

Jeremy Saucier, editor of the American Journal of Play, agrees that people became much more risk-averse, and litigious, in the 1970s. “The ball pit came out of different forces colliding in the ’70s,” he says, including both safety concerns and designers taking an interest in creating different kinds of playscapes. In the 1980s, the idea of softening play became particularly popular. (But as both Solomon and Saucier acknowledge, there was an equal, opposing force driving playgrounds at the same time. After all, adventure playgrounds, unrestricted spaces where kids could play with whatever they found lying around, also gained traction in the 1970s and ’80s.)

By the 1990s, the ball pit was a staple of any children’s pizza parlor. “The ball pit today is a product of the family entertainment center,” Saucier explains. “For most of the 20th century, arcades were seen as seedy, and pinball was linked to gambling and racketeering. Middle-class parents didn’t want arcades in their towns, and Chuck E. Cheese was a response to that — a safe, respectable place that played to current anxieties. The ball pit has always been a standard part of that.” (Interestingly, Saucier points out that it was the co-founder of the arcade company Atari, Nolan Bushnell, who also created the Pizza Time Theatre, the precursor to Chuck E. Cheese. It seems Bushell cleverly played both sides of the arcade vs. the kids’ pizza parlor.)

And it wasn’t just kid-oriented pizza parlors either. The ball pit trend also spread to fast food restaurants catering to young customers, with McDonald’s opening up its first PlayPlace in 1987.

Now that the children of the ’90s have kids of their own, not only are they diving back into the ball pit themselves, but their parenting tendencies are fostering more and more safe indoor playscapes. “Indoor play is very appealing for many Americans,” Solomon says, “and in Asia and Europe, there’s a trend of sanitized play areas, with paid spaces becoming popular miniature cities where children can be firemen, go to the grocery store.” All under the watchful eye of their parents.

“Being indoors changes the whole dynamic,” Solomon adds. “Ideally, play is a public event in a place you don’t pay for, where you come back over and over again,” a place close to home, where neighborhood kids gather independently, regardless of their parents’ schedules. While indoor play spaces gather families from different neighborhoods, they often require a guardian to physically take the kids there and to pay an admission fee, which tends to limit both how kids play and who they play with.

Perhaps it’s the sanitization and standardization of play that made the tenets of soft play so popular in both fast food restaurants in the 1990s and in tech offices today. After all, the same generation that frequented McDonald’s PlayPlace now works for Google and Facebook, with their office ball pits, hanging net swings, and plastic slides.

Although McMillan’s original vision has been largely watered down and corporatized over the years, the overall trend of adults swimming in ball pits seems like something its creator would approve. “I design my equipment for the child in me,” McMillan told People magazine in 1979. “It’s always something I would like to play on — or in. ... If adults played more, there would be far less fear and more understanding, because play is an open and honest exchange.”

Solomon is skeptical of adults playing the same games as children (“Adults should be talking about recreation, not play”), but she was recently taken with a new project in Helsinki, where sloping rooftops provide “parallel play” opportunities for people of all ages. For Solomon, play is all about learning through experimentation, and replaying the same games as an adult doesn’t teach a person anything new.

Saucier, on the other hand, sees the movement toward play for adults in a more positive light, even as somewhat therapeutic. (He notes that ball pits are often used by occupational therapists — albeit mostly with children — to create a controlled sensory environment.) “Ball pits play to Instagram and a sense of loss of a golden age, but their popularity speaks to growing concerns and interest in adult play,” he says. “Tactile play is important, because so much of our lives is digital.” In an era of constant connectivity, when it’s almost impossible to disconnect from work, adult play becomes increasingly important, he says.

As for ball pits in offices, although the goals appear to be a more casual and enjoyable work environment, there’s also a potential dark side: “Some critics have charged companies with creating these spaces to keep employees at work even longer,” Saucier says, “blending time previously separate and set aside for work or play.”

The general resurgence of ball pits is a small part of a much larger trend in returning to the games of childhood. Adult coloring books have also gained traction in the past several years. As have board games and arcades at bars and kid-free summer camps. For adults, these cease to be exercises in learning, instead becoming a kind of escapism (and often paired with alcohol for good measure). “As a historian, I think about play broadly, as something purposeless,” Saucier says. “It is its own reward; it’s voluntary, set apart, and fun.”

So next time you dive into a ball pit and position yourself for the perfect selfie, take a beat to appreciate the fact that what you’re doing should have no purpose. It is its own reward. Then, perhaps, you’ll put down your phone and just savor the moment.

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