Read first, or watch first?
For most families the book comes first here, and for one specific reason: the 1993 film has already answered the question Twain spends the novel asking, so watching first tells your reader how the moral crisis resolves before they've felt it build. If your kid is younger than the book, though, the film is a real door rather than a lesser copy — it's warm, it's PG, and Elijah Wood and Courtney B. Vance are genuinely good together. Just say plainly which parts were changed, because a kid who loved the movie will hit Tom Sawyer's arrival in chapter thirty-three with no warning at all. Whichever order you pick, read the content note first.