In a large punch bowl or pitcher, combine Sprite Zero with kool-aid powder and stir until the powder is dissolved.
Add two large scoops of lime sherbet and stir. You can allow sherbet to melt, or wait put a little in each cup just before serving for more of a float.
Refrigerate until it's time to serve.
Notes
Alternatives: You can substitute Sprite Zero with almost any lemon-lime soda or sparkling water. Store leftovers in the fridge.