Read first, or watch first?
Movie first is fine, and for most kids it's how it will happen anyway; just tell them plainly that the book is not the movie. The 1967 film suits younger kids, the 2016 one is scarier, and neither will spoil the book, because most of the book was never filmed. We've found the simplest audition is to read Rikki-Tikki-Tavi aloud one evening: if it wins them over, the whole collection will.