The Little Girl Who Lives Down the Lane (1976) is a horror/thriller movie about a 13-year old girl with a dark secret. It stars Jodie Foster (as the "little girl" from the title) and Martin Sheen. It was nominated for 5 Saturn Awards, winning 2: best horror film, and best actress. I watched until the emphasis on the much older Martin Sheen making sexual advances towards the 13-year old Jodie Foster got too distasteful. At 13, she was much too young for that to be watchable for me. You can watch it online here.
The NYT calls it "a mild-mannered horror movie for people who don't much enjoy being scared." Rotten Tomatoes has a critics rating of 90%.