This was deliberately set out be a Godzilla film aimed at small children for release during the Christmas season. Among the more unusual aspects of the film was the casting of Hideyo Amamoto as a toy designer and friend to the little boy. Amamoto was normally cast in other films as the slimiest of criminals, gangsters and henchmen.
Much of the imaginary scenes taking place on Monster Island are made up of stock footage taken from various other Godzilla films. However, the scene when Godzilla tries to teach his son how to fire nuclear breath was newly shot instead of being a reuse of an identical scene from Son of Godzilla (1967).
Eiji Tsuburaya was so busy with his company, Tsuburaya Productions, during the production of this film that Ishirô Honda had to take over the effects direction, which resulted in limited special effects work and stock footage. Tsuburaya did not work on the film at all, aside from the stock footage, but is credited out of respect.
The movie was inspired by Gamera movies such as Gamera vs. Viras (1968), which made use of stock-footage shamelessly copied from earlier Gamera entries. Since the Godzilla movie series was performing progressively worse, producer Tomoyuki Tanaka looked at the Gamera films, cheap rip-offs of his once prestigious Godzilla franchise that was still popular among small kids, for inspiration on how to create a Godzilla movie with reduced costs. Thus, he asked scriptwriter Shin'ichi Sekizawa to write a movie based around preexisting Godzilla footage and imitate their own imitator.
After years of playing mainly villains, this was the first time Hideyo Amamoto was asked to play a somewhat fatherly figure in the person of toymaker Shinpei. However, he was not particularly fond of this role.
Director Ishirô Honda intended the movie to have a somber ending, but had to add a more cheerful final sequence in which Ichiro goes to play with his friends. When the movie was re-released on home video during the 80s, Honda removed this scene, so the movie ends with Ichiro's mother crying due to not being able to spend more time with her son.
Often considered the worst Godzilla movie by fans for its childish plot, an annoying child protagonist, its focus on the unpopular monster Minilla who even talks this time, its heavy use of stock-footage from earlier films, and for forwarding a controversial message.
According to the production notes, the monster Gabara is supposed to be a mutated toad, hence why he lacks a tail. His name has had a couple disputed origins: some believe it's a dig at Argentine revolutionist Che Guevara, others say it was based on the German word "Gewalt", meaning "violence".
Despite using copious amounts of stock footage from earlier films, the scene in which Godzilla tries to teach his son how to breathe atomic flame was newly shot. Director Ishirô Honda wanted to avoid simply reusing a very similar sequence from Son of Godzilla (1967), and instead put his own spin on the scene by making Godzilla be more strict with his son this time around. This was part of the movie's theme of paternal neglect and children having to stand up for themselves.