Preheat the oven to 350°F (175°C).

In a mixing bowl, combine watermelon puree, sugar, and butter until smooth.

Add eggs and vanilla extract, mixing well.

In another bowl, whisk together flour and baking powder.

Gradually add dry ingredients to the wet mixture, stirring until just combined.

Spoon the batter into a muffin tin lined with cupcake liners.

Bake for 20 minutes or until a toothpick comes out clean.

In a bowl, beat together cream cheese, powdered sugar, vanilla extract, and watermelon juice until smooth.

Once the cupcakes are cool, frost them with the cream cheese mixture.