Follow the walkthrough until the reincarny goes to bed and you see the dead kids. Then, set the reincarny's bed on fire with the candle.

Follow the walkthrough all the way to the end.

Use the cigarette on the purple demon.

Play the game on halloween, or set your date of the computer to 31 october.

Use a knife (found in the kitchen) and a lit candle (obtained by combining a cigarette and a candle, both found in the living room) on the pumpkin next to the front door of the house.

When you start the game, don't ring the bell.
Instead, click the arrow in the lower right corner to go to the screen with the kids.
Pick up a rock from the pile of rocks to the right.
Then, click it in your inventory and then click the vampire kid.
The demon throws a rock to the kid. Repeat the rock throwing ten times.