Inheritance , method signature , method overriding and throws clause

My Parent class is :

import java.io.IOException;
public class Parent {
        int x = 0;
        public int getX() throws IOException{
        if(x<=0){
         throw new IOException();
        }
       return x;
      }
 }

I extend this class to write a subclass Child:

public class Child1 extends Parent{
     public int getX(){
        return x+10;
   }
}

Notice while overriding the getX method in the Child class , I have removed the throws clause from the method definition .Now it results in an anomalous behavior by the compiler which is expected :

new Parent().getX() ;

does not compile without enclosing it in a try-catch block , as expected .

new Child().getX() ;

compiles without enclosing it in a try-catch block .

But the below lines of code needs the try-catch block .

Parent p = new Child();
p.getX();

As this could be foreseen i.e. using a parent class reference to invoke a child method during run-time polymorphism , why the designers of Java didn't make it mandatory to include the throws clause in the method definition while overriding a particular parent class method ? I mean if a parent class method has throws clause in its definition , then while overriding it the overriding method should also include the throws clause , Ain't it ?