If you feel you must watch this film, go immediately to the doctor; you're deathly ill. On your way to the doctor, stop off at a bookstore and buy "The Crying Child" by Barbara Michaels, one of her best and most imaginative novels and the supposed "basis" for this terrible film. What the director and the production team did to her story is criminal and they all deserve to be prosecuted to the full extent of the law.
This did have potential. Mariel Hemingway fits the character of Mary nicely but would have been much better as Jo, who was her sister in the book; the rest of the cast is okay but not brilliant. The location also fits the story. It's what they did with the material that stinks.
It bears little resemblance to the novel; the central character has been switched from Jo to Mary, her sister. This seriously undermines the story from the first moment. Gone are the estate caretaker and his wife, central characters to the plot and elemental in it's resolution. The character of the doctor has been completely changed. Gone is the gothic texture of the plot and the house itself, which is way too new in the film and not nearly big enough. Gone is the pace of the novel and the binding central story, filled with a rich history that made the novel so enjoyable. In its place is a blind woman, never in the book, who is ridiculously put in as filler to explain everything and then is conveniently killed; no one is killed in the novel. This would have been a great story to shoot as a major motion picture, done in the manner of "The Innocents"; it deserved the muted, horrific feel of that earlier film and the story matter is somewhat similar. The book has tremendous potential and I'd love to see it done right, since it is just about my favorite Michaels story.
If you must watch a film based on a Barbara Michaels book, get "The House That Wouldn't Die" (based on her earliest ghostly novel, the marvelous and haunting "Ammie, Come Home"), a 1970 TV movie that was not perfect but much closer to Michaels own vision. It only cut out a small part of the book and kept the correct story; the cast was perfect and despite its flaws I could accept it as Michaels vision.
Bottom line: Go get the book "The Crying Child" and thoroughly enjoy yourself; don't waste your time with the film. It's a worthless piece of trash and all prints of it should be destroyed to protect the minds of future generations.