In a large bowl, beat the softened cream cheese with an electric mixer until smooth.
Add the powdered sugar and vanilla extract, and mix until well combined.
Gradually add the milk, mixing until the mixture is creamy and smooth.
Fold in the whipped topping until fully incorporated.
In a separate bowl, combine the strawberries, blueberries, and mini marshmallows.
Gently fold the fruit mixture into the cheesecake mixture until everything is well coated.
Chill the salad in the refrigerator for at least 1 hour before serving to allow the flavors to meld.
Serve in individual bowls or a large serving dish, garnished with extra berries if desired.