When the Count is counting the end credits he says "Hi, Mom" when Joan Ganz Cooney's credit appears. Cooney is the creator of Sesame Street (1969) and the founder of its production company, the Children's Television Workshop; she is sometimes referred to as the mother of Sesame Street.
When Big Bird is being welcomed home at the end of the movie, you get a quick glimpse of a character in a window that was definitively Elmo. The movie was made before he was even considered a character on the show.
The newscaster, played by Chevy Chase, opens his broadcast by quoting the theme song from Mister Rogers' Neighborhood (1968), another PBS kids' production which became popular during the same period as Sesame Street.
In the scene where Big Bird asks two children to contact Sesame Street to save him, he asks them to contact Mr. "Looper's" store, meaning Mr. Hooper's store. This continues a running gag from the television show, in which Big Bird would always mispronounce Mr. Hooper's name.
According to Noel MacNeal, after filming the footage of Big Bird on the farm with the kids, the filmmakers discovered that the film was badly scratched and unusable. The actors, crew and performers had to return to the same location, but it was months later and in winter. Many of the green leaves the audience sees are spray-painted, and after each take, the kids would run to put their coats on.
When Big Bird leaves Sesame Street, a sad classical music is playing; it is Antonio Vivaldi's "Concerto for lute, 2 violins and continuo in D Major II - Largo". It was used in a short film (called "Sad Flower Film" by fans) in an early episode of the original Sesame Street (1969), and after being featured in several episodes through the years, that short film was featured in Sesame Street: Episode #15.4 (1983) (Episode #1839), directly after the segment where Big Bird is told by the people of Sesame Street of Mr. Hooper's (Will Lee's) passing, which augmented its sad atmosphere. With that in consideration, the song may have been selected as a fan service, to similarly permeate the sad, dramatic atmosphere of Big Bird leaving Sesame Street.