vanilla ice cream in a bag

I took my kids to Mother Goose Asks Why at the library.  They always do an outstanding job.  This time my kids learned about solids and liquids and this very nice lady demonstrated how to make ice cream in a bag.  You don't need a fancy ice cream maker- just a ziplock bag!

vanilla ice cream in a bag (from the nice lady at the library and inside book Change It! Solids, Liquidfs, Gases and You by Adrienne Mason)
1 cup whole milk
1 teaspoon vanilla
1 tablespoon sugar
1 small sealable plastic bag
1 large sealable plastic bag
12 ice cubes
2 tablespoons salt

Put the milk, vanilla and sugar into the small plastic bag.  Seal the bag.
Place the ice cubes in the large plastic bag.  Sprinkle the salt on the ice.
Place the small bag in the large bag.  Seal the large bag well.
Put on some music and shake the bag for 10 minutes.
Scoop your ice cream into a bowl and enjoy.