public function getChildOrganizations($parentId = null)
    {
        static $children;

        if (is_null($parentId)) {
            return array();
        }

        if (! isset($children[$parentId])) {
            $organizations = $this->db->fetchPairs(
                    'SELECT gor_id_organization, gor_name
                        FROM gems__organizations
                        WHERE gor_active=1 AND gor_has_login=1 AND
                            (gor_accessible_by LIKE ' . $this->db->quote('%:' . $parentId . ':%') . ' OR
                                gor_id_organization = ' . $this->db->quote($parentId) .  ')
                            ORDER BY gor_name');

            natsort($organizations);

            $children[$parentId] = $organizations;
        }

        return $children[$parentId];
    }