Go on a scavenger hunt to have each child find a flat-ish rock or stone. Ask the child what does the shape of the rock look like? What does it remind them of? What can they turn it into? An alien head? A fish?
Use markers to draw on the rocks to draw the details of what they see.
Then get a piece of paper to draw the full scene! Have the children place the rock on the page and draw an outline around it so they know exactly where it goes on the page (this is helpful as they draw because the rock may be pushed around a bit and they might get frustrated if they keep having issues lining everything up). Finish the picture with markers, crayons, or paint.