It's hard to call "The Innocents" a "horror" movie. It's chilling, disturbing, scary, yes. But it's so open ended and left to interpretation that it's not just a simple ghost story. The interpretations of what happened and what was really going on have ranged all over the place since the original story ("The Turn of the Screw" by Henry James). William Archibald and Truman Capote were very careful to not lead the story too much into any one direction so it really is up to you what you think happened.
I was so incredibly impressed with it. Neither of us had ever seen it before but we (unsurprisingly) came to the same conclusions about what we felt happened. If you haven't seen it (even if you aren't a fan of horror) I would highly recommend it.
This was one of those movies that you can be sure would not be made today. I know "they don't make them like this anymore" is so trite... but in this case it's true. It would have to be made more apparent, there would have to be more exposition, there would have to be a big confrontation scene or sex scene or something like that in order for it to sell in today's market. And any of that would absolutely ruin how terse and disquieting the story is. Deborah Kerr is absolutely perfect in this as well, so if you're a fan of hers (I'm sure there is someone out there who is a big Deborah Kerr fan) it's worth it just for her. As a bonus, the boy playing Miles was also in the original "Villiage of the Damned" and several other horror/dramatic films of the time period including "The Hellfire Club" and "The Devil's Own".