Cut the watermelon in half and use a melon baller or spoon to scoop out round or chunky pieces.
In a large bowl, combine the watermelon balls, the entire can of fruit cocktail (including juice), and the can of Sprite.
Add milk and gently stir. Taste and adjust sweetness by adding sugar if desired.
Chill in the refrigerator or serve immediately with ice cubes for a refreshing treat.