Divide the clay into three equal portions.
Place the three portions of clay into the three plastic square containers and flatten the clay. Be sure to spread the clay all the way to the edges of the containers so that the entire bottom surface of the container is covered.
Cut a circle about two inches in diameter into one of the clay surfaces. Remove the circle shape and place it in the center of one of the empty plastic containers. You have just created the lake and island shapes.
Cut a peninsula shape into another one of the clay surfaces. Remove the excess clay piece and place it in one of the remaining empty trays to create a gulf formation.
Cut a narrow, 1-inch strip down the center of the final clay surface. The strip should extend from one edge of the container all the way to the other, flaring slightly at both edges. This shape represents an isthmus, a narrow strip of land with water on both sides. Remove the shape and place it in the center of the final empty tray, leaving the two larger strips of clay behind, which have become the strait formation.
Allow the clay in all six trays to dry, and then paint the clay brown or green if desired to represent the land.
Teach children about the landforms, allowing them to pour blue-tinted water into each tray. Make or purchase land form cards to use alongside the land form trays to label them.