They used something described as "sand glue," the recipe for which I estimate the recipe to be about 10 parts colored sand to 1 part glue based on its extremely crumbly behavior. We're going to enlist the help of Daddy to get a good, thick layer of spray shellac put on to stabilize it so we can actually hang the masterpiece on the fridger.
Just in case the spray fixative goes horribly awry, I took a picture of the fish painting and went ahead and cataloged some of Addy's other recent art pieces while I was at it:
