First performed by The Kids of Sesame Street (1970).
Hit versions by Barbra Streisand (MOR #28 1972), The Carpenters (US #3/UK #53/JPN #1 1973).
(Above is from a 1971 broadcast of Sesame Street.)
From the wiki: “”Sing” is a popular song created for Sesame Street, written by staff songwriter Joe Raposo for the popular children’s TV show. In its initial appearance, the song was sung by adult human cast members of the show (the most frequent lead singer was Bob McGrath), and Muppets, including Big Bird.
“Although Barbra Streisand had an Easy Listening hit with ‘Sing’ (in medley with ‘Make Your Own Kind of Music’) in 1972 with ‘Sing’, Karen and Richard Carpenter first heard the song as guests on ABC television special Robert Young with the Young in 1973. They loved the song and felt it could be a big hit. ‘Sing’ became the debut single off The Carpenters album Now & Then, released in 1973.”
Barbra Streisand, “Sing/Make Your Kind of Music” (1972):
The Carpenters & the Jimmy Joyce Children’s Choir, “Sing” (1973):
http://youtu.be/1rWMlm4Zm8Q
The Carpenters & the Kyoto Children’s Choir, “Sing” live recording (1974):