I know it's not summer yet but this is a great one if you are trying to plan ahead. Here's an easy recipe that doesn't take too long.
For each girl you will need:
1/2 cup milk or half and half )
1/2 teaspoon vanilla
1 tablespoon sugar
1/4 cup rock salt
2 quart sized Freezer Zip-loc bags (could use smaller bags)
1 gallon Freezer size Zip-loc bags
hand towel or winter gloves to keep little fingers from freezing
Mix the milk, sugar and vanilla together in one of the quart sized bags. Seal, removing as much air from the bag as possible. Place this bag inside the other quart sized bag, remove air and seal (double bagging to prevent leaking and insuring success). Put the two bags inside the gallon sized bag along with the ice (we filled the bag with ice) and then about 1/4 cup rock salt. Remove air and seal tightly. Wrap the bag in the towel or put your gloves on, and shake, shake, shake.
This takes 15 minutes or so to freeze.
*Recipe courtesy of skiptomylou.org