Read first, or watch first?
It depends on your reader. The book's first third is a genuine mystery, locked doors and crying in the night, and a film will spoil every reveal, so a child who loves mysteries should read first. But this is also a long, slow book where nothing explodes, and for a reader who needs convincing that the destination is worth it, the 1993 film first is a fair trade: they lose the surprises and gain the will to get there.