I take a 16 oz container of nonfat plain or vanilla flavored yogurt. I mix that in my food processor with a package of frozen strawberries and blueberries. I sometimes add some juice, if the mixture is not thin enough. You can also sweeten it with some honey or raw sugar.
Pour into plastic cups and partially freeze. Then add popsicle sticks and freeze until solid. Store in plastic bags. I like the 2 gallon sized kinds.