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!.
- Fill the large gallon-sized bag half full of ice. Add the rock salt and seal the bag.
- Put milk, vanilla, and sugar into the smaller bag, and seal it.
- Place the small bag inside the large one and seal again carefully.
- Shake, shake, shake until mixture is ice cream, about 5 minutes.
- Wipe any saltwater from ice cream bag before you open it.