The building that housed Hume Cronyn's lunch counter was a unique old building that was the only one on the block. Twenty-five years earlier it was used for the Judy Holliday musical Bells Are Ringing (1960) with the block in the same condition.
The opening montage shows pictures of Frank Riley in a Navy uniform circa World War 2. Later in the movie when his wife pulls out his pocket watch it has a leather fob attached with a gold anchor with a silver "USN" on it, signifying Frank achieved the rank of Chief Petty Officer during his time in the service.
In the scene where Harry is running through Downtown New York with the youngest baby flying saucer. If you look carefully in the background, you can a theater marquee of "The Fly". The film was in production when "The Fly" was released on 15 August 1986.
The trivia item below may give away important plot points.
When the mass of flying saucers appears after the building burns they are arranged as follows: unused prototypes in the front row, cast plastic models in the second and third rows and scaled-down cast models in the remaining rows.