Six and seven going on seventy

My children are Billie (girl, nearly six) and Ben (boy, just turned seven). This morning my husband caught them in some serious conversation. The following was said:

Ben: "Bananas don't go off, they can always become smoothy."
Billie: "That's right, but you should not buy things when other things aren't eaten yet."
Ben: "The mozzarella has gone off, it has turned into water and they (meaning us hapless parents) have three of them."
Billie: "The flies lay eggs in the ham because the fridge lets them in."
Ben: "That is why the mozzarella is off."
Billie: "We don't have money for a new fridge."
Ben: "That is true, they are more than £10."
Billie: "Yes, they cost over a Zillion pounds. You just should not buy more than you eat. The pate is now in a container so it doesn't go off."
Ben: "That's right, because it's got Brussels sprouts in it."
Billie: "Oh ..." - giving some deep thought to how Brussels sprouts (which she doesn't really like) get mixed into Brussels pate (which is her absolute favourite).