The film follows Van Dyke as inventor Caractacus Potts.1 His children implore him to purchase an old junk racer and fix it up. Thus Chitty Chitty Bang Bang (the car) is born. The children's wild antics lead him to a adversarial/loving relationship with the wealthy Truly Scrumptious.2 The car however draws the attention of Baron Bomburst, ruler of the barony of Vulgaria.3 The Baron mistakenly kidnaps Grandpa Potts, and the quartet of heroes is forced to rescue him.
Though the Baroness is clearly a villain in the film, her only real crime is desiring a land without children, a position with which I can sympathize. Of course, her desire to be rid of children may be due to the childish antics of her husband, who she loves dearly anyway.4 The comical nature of the villains and the cheery songs makes Chitty Chitty Bang Bang an overall enjoyable film from my childhood that I still enjoy today.
1. It's a pun you see, Caratacus Potts --> Crack Pot... Very clever naming in this film.
2. Played by Sally Ann Howes. Of course, this name is another pun. Truly Scrumptious in addition to being an absolute delight is also the daughter of a confectioner.
3. Yet another pun! Vulgaria --> Vulgar. Oh what piquant wit. Bomburst is either a reference to bombs bursting, as the Baron has an explosive temper, or a pun on "bombastic" which also fits with his personality. The Baron is superbly portrayed by Gert Fröbe.
4. The Baron and Baroness Bomburst almost have a Al and Peg Bundy type relationship, where she is a relatively attractive woman whose plain husband has no desire for her.