Ice Cream in a Bag - for Kids!
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You may have to experiment with this a bit first.  Humidity and outside temps can change the recipe's results  If you are doing this with little ones, they probably need to wear gloves, as the bags can get quite cold.  For your sanity, you probably want to take this activity outside!.     
When children (and even teens) are helping in the kitchen, always use safety first as your motto!
​Supervise carefully and pay attention to details.   Remember - YOU are the responsible one.
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Ingredients for each child's serving bag
1 tablespoon sugar 
1/2 cup milk or half & half
1/4 teaspoon vanilla
6 tablespoons rock salt (in a pinch, you can use water-softener salt pellets)
1 pint or quart-size Ziploc plastic bag
1 gallon-size Ziploc plastic bag
ice cubes
Steps
  1. Fill the large gallon-sized bag half full of ice.  Add the rock salt and seal the bag.
  2. Put milk, vanilla, and sugar into the smaller bag, and seal it.
  3. Place the small bag inside the large one and seal again carefully.
  4. Shake, shake, shake until mixture is ice cream, about 5 minutes.
  5. Wipe any saltwater from ice cream bag before you open it.​
To be honest, this will be a bit softer than "real" ice cream, but kids just love the fun of making it!  You can try making sherbet with fruit juice, as well.