A sandpit or sandbox is a low, wide container or shallow depression filled with sand in which children can play. Many homeowners with children build sandpits in their backyards because, unlike much playground equipment, they can be easily and cheaply constructed. In North America a "sandpit" may also denote an open pit sand mine.
Sandpits encourage the imaginations and creativity of children by providing the materials and space to build structures such as sandcastles; use toy trucks, shovels, and buckets to move the sand around; dig holes and bury things, etc. In other words, the sand provides a medium in which children can pretend to explore, construct, and destroy the world in three dimensions. This idea of being creative and experimentation is what the metaphorical uses of the word 'sandpit' or 'sandbox' were born out of.
The "pit" or "box" itself is simply a method of storing the sand so that it doesn't spread outward across lawns or other surrounding surfaces. Boxes of various shapes are often constructed from planks, logs, or other large wooden frames that allow children easy access to the sand and also provide a convenient place to sit. Nevertheless, small sandpits are also available for purchase. These are usually made from plastic and are often shaped like an animal or other familiar object. They also sometimes have lids, to cover the sand when children aren't using it, thereby preventing passing cats from using the play area as a litterbox. Having lids also prevents the sand in outdoor sandpits from getting wet when it rains, although some dampness is often desirable as it helps the sand hold together. Prefabricated sandpits may also be used indoors, especially in day cares. Rather than sand, other materials are also often used such as oatmeal which are necessarily non-toxic and light enough to easily vacuum.
Sandpits can have a solid bottom or they can be built directly onto the soil. The latter allows free draining (which is useful if the top is open) but can lead to some contamination of the sand with soil if the children dig down to it.
The sand gets dirty over time and is eventually replaced. The old sand can be discarded or it can be used for other things (for example, mixed into concrete). Some may use ordinary building sand to fill sandpits, while others use special sandbox sand. Since it is not washed, building sand is far cheaper but often contains materials such as clay that can stain clothes. It will also contain a mixture of grain sizes and colors, and hence will have less appeal to the eye. Ordinary building sand may be strained with a sieve and washed to remove clay and particles to create a cleaner play surface. Many schools and playgrounds around North America have replaced sand around play structures with a wood chip mixture, as it is cheaper and does not stain clothing.