Question regarding overriding methods with sealed class/interface parameters

Main.java

public class Main {
    public static void main(String[] args) {
        // These are objects of the only 2 classes that implement Parent
        // `sealed` defines that there can't be any other classes that implement Parent
        Child1 child1 = new Child1();
        Child2 child2 = new Child2();
        // I can call myMethod(child1) and myMethod(child2) on myClass
        MyInterface myClass = new MyClass();
        myClass.myMethod(child1);
        myClass.myMethod(child2);
        // I can also call myMethod(child1) and myMethod(child2) on myInterface
        MyInterface myInterface = new MyClass();
        myInterface.myMethod(child1);
        myInterface.myMethod(child2);
    }
}

sealed interface Parent {}
record Child1() implements Parent {}
record Child2() implements Parent {}

interface MyInterface {
    void myMethod(Parent parent);
}

// Why can't I override myMethod(Parent parent) with myMethod(Child1 child1) and myMethod(Child2 child2)?
// This should be exhaustive, since Parent is sealed and there can't be any other classes that implement Parent
class MyClass implements MyInterface {
    //@Override
    public void myMethod(Child1 child1) {
        System.out.println("Child1");
    }

    //@Override
    public void myMethod(Child2 child2) {
        System.out.println("Child2");
    }

    // Why is this method needed after declaring the two methods above?
    @Override
    public void myMethod(Parent parent) {
        if (parent instanceof Child1) {
            myMethod((Child1) parent);
        } else if (parent instanceof Child2) {
            myMethod((Child2) parent);
        }
    }
}