Little Sweetheart (1990)

Nine-year-old Thelma (Cassie Barasch) is stuck at her family's vacation house, bored, lonely and perhaps a bit disturbed. So instead of spending time with her relatives, she befriends neighbor Robert Burger (John Hurt), who gives her a camera. But the conniving Thelma has sinister intentions and uses the gift to photograph the married Robert with his mistress, Dorothea (Karen Young), and blackmail him. But as Thelma's little game escalates, it takes a violent turn.