Like childhood itself, ball pits are exciting and colorful and occasionally scary—and they're always an adventure. 

Today, they're a playground staple thanks to designer Eric McMillan, the creator of the original “ball crawl” and the man considered to be the “founder of soft play.” He installed his first playground in the early 1970s after being disenchanted by traditional play structures, which he described to People in 1979 as "architectural graveyards—gray asphalt slabs. They've been built by adults who've forgotten how to play.” 

McMillan built the first ball pit for Sea World's Captain Kids World in San Diego in 1976. Jack Pentes, another soft play pioneer, told The Washington Post that the concept was initially developed in Europe as a therapy for disabled children: "The sensation of all those balls on their bodies would lead them to try and improve their movement." (Before that, the balls were used for holding heat in swimming pools and trapping pollutants in smokestacks.) It’s possible that this is where McMillan, who came from England, found his inspiration. 

McMillan, who would go on to design Sesame Place in Langhorne, Pennsylvania, developed his concept for soft play spaces because he wanted to inspire activity. The play spaces he built throughout his career, he told People, are designed to appeal to his inner child. "A child needs play areas he can affect directly with his senses and curiosity," McMillan said. "To a child, play and learning are the same process." 

The legacy of the ball pit lives on today, for children and grown-ups alike. Just this year, in fact, ball pits for adults have popped up in D.C., New York, and London. While those exhibits might seem like a frivolous concept, they're actually in line with McMillan’s beliefs. 

"If adults played more," McMillan told People, "there would be far less fear and more understanding, because play is an open and honest exchange.”