Continuity mistake: Truly crashes into the pond three times: first when the kids are playing in the road and she takes them home, second on the day of the picnic when she says she has nothing else to do and will go on the picnic too, and third at the end of the film when Potts finds out he is rich. In the second of these three, when Mr. Potts carries Truly from her car in the pond, the end of the ribbons on the back of her dress gets soaked in mud, but when you see her again at the beach there is no sign of the dirt.
Continuity mistake: Dick Van Dyke is trying to show his new whistle sweet to Mr Scrumptious, the sweet factory owner. His dog is tied up to a bicycle outside. When his dog hears the whistle he knocks over the bicycle whilst trying to get free and runs up the steps. In the immediate shot following the bicycle is standing up again.
Revealing mistake: In the scene where Chitty is taking off from the castle, Caracticus looks down at the toymaker and Peter and says, "Bye bye". If you look closely, right in front of them, a boy runs across holding a stick he stole from one of the cavalrymen. He is waving it around and you can tell it's fake because it flops around like rubber. (02:16:50)
Revealing mistake: During the "Toot Sweets" number in the factory, the cart with the candy trays move freely, however later on when they start spinning on them in circles (right after Jeremy gives Mr. Scrumptious another sweet) you can see each one is spinning due to a pole holding it. You can see it just under the bottom trays.
Visible crew/equipment: Right when the doors open, you can see the pulley that's pulling the far door open.
Other mistake: When Professor Potts bought Chitty from the Junkman and brings the car into the garage, the body of the car is charred or damaged somehow from the crash and fire. But the leather seats, dashboard and wooden steering wheel are completely unharmed.
Visible crew/equipment: In the scene where Chitty Chitty Bang Bang comes into the castle to rescue the family, the shot shows the car turning, but a pivot wheel under the car can be seen, and the actual tire while turning, does not match the radius of the turn nor the speed at which it should be rolling.
Factual error: After they pick up Truly Scrumptious in the newly refurbished Chitty Chitty Bang Bang, look at the road surface as they run alongside the GWR train. There is a broken white line running down the centre of the road. These types of markings weren't introduced in England until the blackouts of WW2.
Continuity mistake: Chitty's front wheels are badly damaged in the crash, but are near perfect when Caractacus brings the car home.
Visible crew/equipment: When Caractacus is being dragged across the ground by the rockets, the wire he is holding onto is visible.