Basically it is sand with other ingredients added to end up with a soft and crumbly texture that will hold it's form when squeezed or moulded.
The version we use is sand, cornflour (or flour), and oil.
The cornflour gives a more silky texture than normal flour but both work.
Ingredients (4:2:1 ratio)
2 cups of sand
1 cup cornflour
1/2 cup vegetable oil
Mix the sand and cornflour together until completely incorporated now pour in the oil. Add food colouring or paint powder if you would like. Mix thoroughly until the oil is fully mixed with no dry spots. Now it's time to play!
Use hands, moulds, biscuit cutters, cups, & utensils, include animals, dinosaurs, or anything else you think of. Let your creativity flow.
Ask open ended questions about what the children are making and imagine the sand to be. Talk about the texture, how it feels when they squeeze it or dig a utensil into it. Does if flow / fall out of their hands or stick together? Do dinosaurs leave footprints?