You have this conversation with your six-year-old on the way home from school:
Me: I need to stop at the letterbox on the way home to post these letters.
Flea: Can we write a letter to the PR, Mummy?
Me: Which PR?
Flea: You know, the one who sends us stuff.
Me: Why do you want to send a letter to the PR?
Flea: Because I want some Harry Potter Lego.
I think it's well past time for me and Flea to have bit of a chat about the concept of actually BUYING stuff.