Add the watermelon granita ingredients to a blender and pulse until smooth. Pour into a baking sheet and freeze for 2 hours.
Add the kiwi granita ingredients to a blender and pulse until smooth. Pour into a plastic container and freeze for 2 hours.
Once granitas are frozen, remove from freezer and scrape using a spoon. Scoop watermelon granita into 6 serving glasses, then top with kiwi granita. Serve immediately.
Notes
These can be made kid friendly, just skip the vodka. Be sure you use a touch of honey in its place to help keep the granita from freezing solid.