Here's a quick little activity you can do with your class for fun, or as a science experiment, or with your own kids after school is out.
1 tbl sugar
1/2 cup whole milk
1/4 tsp vanilla
about 1/2 c. rock salt
sandwich or quart size zipper bag
gallon zipper bag
ice cubes or crushed ice
*Fill the large bag half full of ice, and add the rock salt. Seal the bag.
*Put milk, vanilla, and sugar into the small bag. Seal the bag.
*Place the small bag inside the large one, and seal it again carefully.
*Shake until the mixture is ice cream, which takes about 5 minutes.
*Wipe off the top of the small bag, and then open it carefully.