Originally written by Raposo for Sesame Street, "Sing" had been a minor hit for Barbara Streisand in 1972. The Carpenters had not heard the song until they guested on an ABC television special, Roger Young with the Young, where the cast performed it. The duo loved the song and felt it fitting for their next album, despite the fact that most of their associates thought they were "nuts" for doing so.
The Jimmy Joyce Children's Choir was featured on the studio recording of "Sing", but for many Carpenters concert performances, they would invite local children's choirs to sing with them; versions of the song have been recorded in partial Spanish and Japanese.
- Karen Carpenter – lead and backing vocals, drums
- Richard Carpenter – backing vocals, keyboards
- Joe Osborn – bass guitar
- Tom Scott – recorders
- The Jimmy Joyce Children's Choir – backing vocals