
Props: The bike itself was inadvertently helpful in adding to the atmosphere of the location which in itself was spooky (misty, isolated etc) by squeaking (not designed but a good result nonetheless) slowly as it went up the drive. We also chose to use a bike as someone of Liam's normal age wouldn't usually drive a car but this helped us too, as the length of time taken to get up the drive plus the quietness from the bike added also to the atmosphere. The pizza bag, although it wasn't actually a pizza delivery bag, served the purpose of showing he was actually delivering something as opposed to just visiting, and the pizza box, when it came into shot made it clear what he was bringing.
The Girl

Props: we were planning on using a teddy bear but we couldn't get one so instead we went with a lamb which we hope had the same effect - again this built the notion that she was a young child.
The Father
Costumes: we chose a formal outfit for the Father to give the impression that he had been working - the top button being undone but a shirt and tie with formal trousers on suggests he has just come home from work and is taking delivery of his pizza. You can get the impression he lives on his own at the house (despite the size of the property) and you can imagine he just exists there, not really cooking but surviving on take-aways and just about going to work every day. Seeing someone along in a house of that size increases the empathy you might have for him.
Props: the Father has no real props (the house comes under location) as the costume stands alone to indicate who he is.