Profoundly Bizarre & Creepy Australian or New Zealand Film

I saw a movie with a profoundly creepy, almost psychadelic score with flutes and woodwind instruments, I think it was about missing children at an orphanage or school in Australia or New Zealand (or similar) and might be said to have walked the line between horror and science fiction and is almost certainly from the 1970's but possibly a bit earlier or later, the score is so excellent as it is set to the film that this film must have a cult following of some sort but I have not managed to rediscover the title after repeatedly attempting to do so.

Maybe Picnic at Hanging Rock:

Yep, good stuff.