Unable to Cast from Parent Class to Child Class

A simple way to downcast in C# is to serialize the parent and then deserialize it into the child.

 var serializedParent = JsonConvert.SerializeObject(parentInstance); 
 Child c  = JsonConvert.DeserializeObject<Child>(serializedParent);

I have a simple console app that casts animal into dog, using the above two lines of code over here

The instance that your base class reference is referring to is not an instance of your child class. There's nothing wrong.

More specifically:

Base derivedInstance = new Derived();
Base baseInstance = new Base();

Derived good = (Derived)derivedInstance; // OK
Derived fail = (Derived)baseInstance; // Throws InvalidCastException

For the cast to be successful, the instance that you're downcasting must be an instance of the class that you're downcasting to (or at least, the class you're downcasting to must be within the instance's class hierarchy), otherwise the cast will fail.

You can't cast a mammal into a dog - it might be a cat.

You can't cast a food into a sandwich - it might be a cheeseburger.

You can't cast a car into a Ferrari - it might be a Honda, or more specifically, You can't cast a Ferrari 360 Modena to a Ferrari 360 Challange Stradale - there are differnt parts, even though they are both Ferrari 360s.