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.
Factual error: There is a scene where Chitty is pacing the train, which is an 'Austerity' tank engine. This engine was made during WW 2 but the movie takes place in the early 1900s.