Like several other Disneyland attractions, "it's a small world" originated with the 1964/1965 New York World's Fair (it was Pepsi's pavilion.) After the fair closed the ride was transferred to Disneyland and when the other parks opened they too included versions of the ride. The attraction was designed by Mary Blair, who was also an art director on several Disney animated features (including Cinderella and Peter Pan). Like many Disneyland and Walt Disney World attractions, scenes and characters were designed by Marc Davis, while his wife, Alice Davis, designed the outfits of the dolls.
The name of the ride was originally "children of the world". When Walt Disney demonstrated it to songwriters the Sherman Brothers the ride's soundtrack featured numerous national anthems all playing at once. Disney said, "I need one song." In response, the brothers wrote what would be known as the most performed and translated song on earth: "it's a small world".