I am thinking of bring snow in for my K and 1st grade and letting them build a snow castle. Now sure if it would work. I have large pans I use for plaster casting. I may test that out today since it is snowing. I also read a Little House in the Prairie Cookbook and read about maple candy they made by pouring onto snow to cool. I then cross searched it and found a recipe where you boil maple syrup and then place it in a crock pot and have the kids spoon it onto shaved ice. I may test that out maybe they could create poured designs? let you know how that works.
Another idea I found I am going to try is from dick blick chocolate molds. I cannot find it online but in the recent catalog they have a lesson using clay to create a chocolate mold. While searching the site they have new video workshops that are worth checking out.