Short and to the point, this is how my 8-year-old son D- and 5-year-old daughter M- spend much of their free time:
M- (her part of some random chit-chat I'd tuned out): ...duty.
D- (starts to laugh): Wait, do you mean the FUNNY "doody", or the normal, serious "duty"?
M- (almost disappointed in herself): The serious one.
D- (soberly): Oh.
You may enjoy my previous D- conversations, M- conversations, and (wife) J- conversations, as well as my future (<2YO son) E- conversations.