The love child of horchata (the creamy Mexican rice drink) and a piña colada, this drink is fine with or without rum, so kiddos can have a fun drink, too.
In a blender, blend the rice, dates, cinnamon sticks, a pinch of salt, and 4 cups water until the rice is coarsely chopped, about 1 minute. Let soak at room temperature for 4 hours or refrigerate overnight.
Return the blender to the base. Puree the rice milk until smooth, about 1 minute; using a fine-mesh strainer, strain into a large bowl. Rinse out the blender. Return the rice milk to the blender. Add the chopped pineapple, coconut milk, and sugar. Blend until the drink is smooth, about 1 minute.
Divide the drink among 8 glasses filled with ice. Stir 1 oz. rum into each glass (if using). Garnish with pineapple wedges and cocktail umbrellas (if using).