Create a canyon

I want to demonstrate how a canyon is formed, using a flow of water, for second and third graders. any ideas?

Hi,

I would either get a box or a large pan of some sort, and fill it halfway with dirt and rocks (make it even). Then attach a hose from the top of the pan and let the water trickle throughout it. Either do the demonstration live, or take pictures as the water slowly erodes the dirt.