If you kill both sets of parents, leaving the kids with Mr. Harris, you can later kill Mr. Harris, and then the children will continue to live in Mr. Harris's house among his corpse and speak about him as if he were alive even with his corpse in front of them in pieces.
If you complete the confrontation with the Families on friendly terms, you should now notice that Old Man Harris' doors are locked, yet no one seems to hold the key. To unlock the door of Old Man Harris' house, if on friendly terms with the families, you have to kill the families to unlock the door. (Confirmed on Xbox 360, PC & PS3.)
If you enter the Smith's basement, discover the truth behind the strange food and then exit the Smith's house you will notice the Smith and Wilson parents stalking towards the Smith's front door as if they don't notice you had already exited. After Jack Smith gets to his own front door he turns to confront you with the usual dialogue. (Confirmed on PS3 and 360).
If you enter the Smith's basement, etc, the four adults gather in around the front door of the Wilson house as if they expect you to emerge from there instead. If you go up to them, the cut-scene plays out as normal. (Confirmed on Xbox 360.)
If you enter the shed and exit, the adults will immediately engage in conversation with you. If you quickly fast travel to Andale, teleporting to the center of the town, you will still be engage in dialogue sequence with Mr. Smith despite being 50 feet away from him.
Occasonally, after you exit the shed and talk to Mr. Smith, the residents will be stuck in their combat phase and wont move unless you attack them. (Confirmed on PS3).