Preheat your oven to 350°F (175°C) and line a 12-cup muffin tin with cupcake liners.
Cream together the softened butter and granulated sugar until light and fluffy.
Add the eggs one at a time, mixing well after each addition. Stir in the milk and vanilla extract.
In a separate bowl, whisk together the flour, baking powder, baking soda, and salt. Gradually add to the wet ingredients, stirring until just combined.
Gently fold in the diced mango and strawberries.
Divide the batter among the cupcake liners, filling each about two-thirds full. Bake for 18-20 minutes.
Allow the cupcakes to cool in the tin for about 5 minutes, then transfer to a wire rack to cool completely.
Prepare the frosting by beating together the powdered sugar, milk, and vanilla extract until smooth and creamy.
Frost the cooled cupcakes and garnish with fresh fruit slices if desired.