This is recommended for older children, as the mixture may be too rough for little fingers to mold.
2 cups clean sand
1 cup cornstarch
1 cup water
Slowly heat the mixture in a heavy pot, stirring occasionally, until thick (about 30 minutes). Turn the thickened mixture out onto a cookie sheet or shallow cardboard box. Work with it immediately. Allow finished pieces to dry for 24 hours or set them in a cool oven (200 degrees) for 4 hours.
Turn off oven, open door, and let pieces finish drying for another 4 hours.
Finish by sanding rough edges with an emery board. Add fancy details such as flags, trims, bushes, etc. with white glue.