I somehow happened upon and decided to watch "The Girl Next Door" (2007), which is also known as "Jack Ketchum's The Girl Next Dooor." Please note that this is not the film with Elisha Cuthbert and Emile Hirsch.
This film is "inspired by actual events" and is based on the story of two adolescent girls who are sent to live with their aunt after their parents die. The aunt and her children abuse and torture her nieces. It also involves a neighbor boy who befriends the nieces and shows how he struggles to prevent and rescue the girls from their torture.
I have mixed feelings about this movie. I thought it was decent/pretty good, but at the same time heart-wrenching and horrifying. It grabbed my attention from the beginning and didn't let go. I wanted to stop watching it jut because I didn't want to see that form of "child abuse," but I had to know it ended.
There is another movie called "An American Crime" that is supposedly more true to the real story, but I have not seen it.
I didn't read the Wikipedia or TruTV's Crime Library stories regarding the actual events before watching the movie. I would recommend you avoid them as well. But here they are if you want to read about the story without watching the movie. I think they are both worth reading. The links are in the spoiler tag.