According to Robert Osborne on TCM, this was a film that Jack Lemmon didn't really want to do, but he fulfilled a contract with the studio. And like the previous year's "Under the Yum Yum Tree", this stupefied Lemmon that they were both very successful films.
The "old fashioned grandmother" drives the children to camp in a 1963 Corvette hardtop roadster.
The name of the advertising firm for which Sam Bissel works, Burke & Hare, is clearly a reference to William Burke and William Hare, two Irish laborers living in 18th century Edinburgh, Scotland who became notorious as history's most famous "body snatchers" who, until they were discovered by the British authorities, killed at least 15 travelers and then sold their corpses to medical schools for dissection.
The phrase "in the middle of the night" is used 8 times, starting 57 minutes into the movie.