Factual error: In every version of the story, including the book, in the scene where Augustus Gloop is sucked into the chocolate pipe, there's no pressure below him (it's an open river, with the pipe sticking into it) so the pressure must come from a vacuum at the top of the pipe. Augustus would have had his lungs and innards sucked out until he was thin enough to pass through the pipe. He would not have survived.
Other mistake: When the boat that Willy Wonka and the passengers are riding on is heading for the tunnel through the river of chocolate, two crewmen are cranking the paddle wheel. The wheel is in an opening in the middle of the deck. As the paddle is rotating, moving the boat through the river, the blades are always clean and dry and never have any chocolate on them whatsoever. Also the paddle is rotating the wrong way. It should be rotating clockwise.
Visible crew/equipment: There is a cameraman shooting near the gate of Wonka's factory: he is strategically placed to get up close shots shown in the movie yet he blends in to the crowd to make the movie audience think he is one of the many media technicians filming the event of Wonka opening his factory. Later, when the guests are passing through the gate, the cameraman has disappeared.