Little Sweetheart (1988)

Having embezzled a small fortune and attempting to lay low, Robert Burger (Sir John Hurt) and his mistress Dorothea (Karen Young) choose a remote rental property which is unobtrusive. They soon make the grave mistake of befriending two nine-year-old girls, Thelma (Cassie Barasch) and Elizabeth (Ellie Raab), who live close by. Behind her seemingly cute and innocent façade, Thelma is a scheming, precocious brat who intrudes upon the couple's life and photographs the pair and ultimately discovers their dark little secret. With Elizabeth's help, they proceed to blackmail the bemused, unsuspecting twosome. But events eventually begin to unravel leading the pseudo-angelic brat to resort to twisted and evil crimes, meaning the lives of those associated with her gradually descend into Hell.