The first time I made this Charlie was in bed, I let Harper take it outside, he played for over an hour by himself, each time I went to check on him he taken off another layer of clothes, he ended up almost naked so I made him come inside (it's winter here), then the phone ran.
Long storey short.
He came inside then started throwing the dough all over the laundry, then he spilt the dogs water. I got off the phone and spent over an hour cleaning. Do you know what happens to flour when it gets wet? If you don't, you don't want to.
My point being, unless you can deal with the mess I recommend keeping it outside.
8 cups of plain flour
1 cup of oil. For younger kids I use vegetable oil, for older kids you can use baby oil (it smells incredible but you don't want a baby eating baby oil )
It turns out like sand but softer, its light and crumbly but mouldable. A sensory dream.