At Walt Disney World Resort in Florida, a huge chorus of the song was performed in front of Cinderella Castle at Magic Kingdom by cast members and a children's choir from Central Florida Performing Arts.
The kids - who didn't seem to mind belting out several takes of what some consider an earworm - sang for a live broadcast on "Good Morning America." Tributes to the song will also be held throughout the park all day, and other parks around the world also held sing-alongs.
Not that the parks are in short supply of the song on any regular day. Disney officials estimate that during a 16-hour operating day, the song is played, on average, 1,200 times.
It was written by Richard and Robert Sherman at the request of Walt Disney himself. The brothers won Academy Awards in 1965 for the music for "Mary Poppins."
The "It's a Small World" song and animatronic attraction debuted at the 1964 New York World's Fair. It was shipped to Disneyland in California then recreated at the other Disney parks. The attraction opened at the Florida park in 1971.
While some adults may complain about the infectious nature of the song, the gentle boat ride is a calm and air-conditioned respite from the crowds and heat - and little kids love it.
With its hundreds of costumed dolls, the attraction was considered high-tech back in the 1970s. It's definitely different than many of the other new theme park offerings these days. There's no 3D, no complicated storyline.
"I think 'It's a Small World,' because of the message that it brings, really does resonate with the audience," said Gary Landrum, a Walt Disney World Imagineer and archivist from California. "It was really one of the first of what became the classic Disney theme park attractions. It's a beautiful story, it's a simple story that I think the public really connects with."
On Thursday morning, Chris Pini, his wife and their two children raced to the Small World ride first thing.
"I came down here as a kid and rode this with my parents, and now I'm getting the chance to take my kids on it," he said. "It's awesome, I know it's been around here for 50 years and it's an amazing ride."