mysql on delete cascade

I been trying to run this example but the constrains are not holding

CREATE TABLE parent (
  id INT NOT NULL,
  PRIMARY KEY (id)
);

CREATE TABLE child
(
 id INT,
 parent_id INT,
 FOREIGN KEY (parent_id) REFERENCES parent(id)
 ON DELETE CASCADE
);


If I delete the parent_id from parent then any id match the deleted id should be deleted from the child table but it is not  Please advice!

Thanks