- Dawson Casting:
- Margery Gray was in her early 50s when she provided the voice for Heidi.
- Roger DeWitt, Jr., Peter's voice actor and the real-life son of Jean Vander Pyl, was only 18 years old when he voiced the 11-year-old Peter.
- Fake Nationality: While Heidi's Song is set in Switzerland, nearly all of the cast are played by either American (Margery Gray, Roger DeWitt, Jr., Richard Erdman, Joan Gerber, Virginia Gregg) or Canadian actors (Lorne Greene). However, it's averted with Fritz Feld (Sebastian), who was German like his character.
- Real-Life Relative: Like most Hanna-Barbera shows of the era, writer and producer Joseph Barbera's daughter, Jayne, served as the production supervisor.
- Release Date Change: Heidi's Song was originally set for release in late 1976, before it was pushed back to late 1977 as it was still in the preparatory stages at the time. It was later due for release in 1981 and eventually, the film was released on November 16, 1982.
- What Could Have Been:
- Originally, Heidi was going to be voiced by a young child. However, veteran stage actress Margery Gray ended up voicing her instead.
- Taft International Pictures, which was the film division of Hanna-Barbera's then owner, Taft Broadcasting, was originally going to distribute the film before Paramount picked up the distribution rights.note
- Songwriters Burton Lane and Sammy Cahn originally planned 20 songs for the film in its early stages, but only 16 songs were included in the final version.
Trivia / Heidi's Song