Revealing mistake: As Vicky and Burt are driving down a dirty lane, through a row of corn, you can see fresh tire tracks in the mud from a previous take. (00:34:35)
Revealing mistake: When Vicky throws the lamp at the children, there's no power cord attached to it.
Revealing mistake: When Burt hits one of the children, the skid marks are in front of the car, when they should be behind it.
Chosen answer: Who knows? Maybe they blackmailed her, because she works there, and the children wouldn't get caught poisoning the coffee, or maybe she isn't as old as you think, she could well be in her mid 20's, it's hard to tell, you only see her briefly.
Hamster ★
She is obviously in her late teens, early 20s.