Remove the pit from the cherries. Put them into a blender. Add 1 tbsp of the simple syrup, 1 cup of sparkling water, half of the lemon juice (reserve the other half for step 2) and 1 cup of crushed ice. Blend all the ingredients and set aside in a bowl.
Put the chopped peaches into the blender. Add 1 tbsp of the simple syrup, half of the lemon juice, 1 cup of sparkling water, and 1 cup of crushed ice. Blend all the ingredients and put the mixture in a bowl.
Put the two bowls in the freezer. Freeze for 30 or 60 minutes. When it begins to turn into ice, scrape the mixtures with a fork and freeze again for another 30 or 60 minutes. Repeat the process one or two times more.
Assemble by layering the slushie mixture in a glass.
Frozen peaches and frozen cherries can be found in the freezer section of your local grocery store. Using frozen fruit for this drink is your best course of action as it adds to the slush factor!