Supernatural (TV series)/Recap/S04/E11 Family Remains

Season 4, Episode 11:

Family Remains
Sam and Dean investigate the appearance of a young female murderous spirit inside the walls of a suspected haunted house. Complications ensue when a family of five moves in, and the "spirit" turns out to be two very non-supernatural, feral children who are the product of incest and years of abuse, and who are willing to kill to protect their home.

Tropes

 * Call Back: The rescue in the walls is very reminiscent of No Exit from season 2.