Returns child IDs of the given parent category

        :param str parent_alias: Parent category alias
        :rtype: list
        :return: a list of child IDs

def get_child_ids(self, parent_alias):
        """Returns child IDs of the given parent category

        :param str parent_alias: Parent category alias
        :rtype: list
        :return: a list of child IDs
        """
        self._cache_init()
        return self._cache_get_entry(self.CACHE_NAME_PARENTS, parent_alias, [])