It seems the parent class method throws any child or sibling of RuntimeException, and the child throws RuntimeException this is ok.
RuntimeException is unchecked. Your child can throw any unchecked exception irrespective of whether the parent throws any exception.
when parent class method throws any child or sibling of RuntimeException, and the child throws Exception this is not ok
Exception is checked. If the child throws a checked exception then this has to be the same or a subclass of the exception thrown by the parent.
John