We discussed each layer: the inner core, the outer core, the mantle and the crust.
I then showed them a playdough Earth I had made the night before and proceeded to cut through to see the various layers. (Of course, this gave us a chance to discuss knife safety!)
We passed around the two halves and pointed out the different layers.
After the presentation, many children chose to make their own Layers of the Earth booklet.
One child also pin-punched each layer and glued on to make a little diagram.