I agree with HollyS. We have always had a rule that we would not watch the movie version until after we finished the book. The question always came up about how the movie compared to the book.
I recall watching the movie, Rascal, after we finished Sterling North’s book. My kids were 10, 9, and 8. We thoroughly enjoyed the movie, but at the end, all of my kids were rather irate that a brief scene was added when Rascal was released back into the wild. Certain details in the scene varied greatly from the book, and my son hollered, “Hey! That wasn’t in the book! How rude!!”
We’ve always had great discussions about how movies are made and how details sometimes are changed to fit time constraints, etc. We decided as a family that, although the BBC’s version of The Railway Children was good, they had to leave a lot out of the movie because there was just so much in the book. The movie would have been hours and hours long if they included every chapter.