Staley: "Daddy, why do you have to go to work?"
Zach: "When we go to a store to buy something, what do we need to give to the person at the check-out?"
Zach: "That's right. We have to use money to buy things like our house and our car and food and clothes and toys. When Mommy and I go to work, we get money and that's how we buy the things we need."
Staley: (long pause as she's thinking) "So when you go to work tomorrow, you could stop and buy me another mermaid."
Unfortunately, I think she's got a good understanding of how this money thing works...and how her Daddy operates.