01 - Combine watermelon, mango, and lime juice in a blender. Process until completely smooth, scraping down sides as needed.
02 - Divide the fruit puree evenly among 4 tall glasses, filling each about one-third full.
03 - Pour ½ cup chilled lemon-lime soda into each glass. Stir gently with a spoon to incorporate while maintaining some effervescence.
04 - Place one generous scoop of vanilla ice cream on top of each drink, allowing it to float on the surface.
05 - Add fresh mint leaves to each glass if desired. Serve immediately with straws and long spoons for stirring.