Blend the watermelon the day before and store in the fridge.
Garnish each drink with a slice of watermelon and kiwifruit. If you like, moisten rims of the glasses and dip in coarse sugar crystals, then fill with watermelon lemonade.
Don't worry if you find a few seeds in your watermelon. Seedless watermelons actually do have a few seeds; however, they are usually small and edible and will be virtually undetectable by the time you blend the mixture.