function add_children( $post_id ) {

                if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE )
                    return;

                if ( !wp_is_post_revision( $post_id )
                && 'page' == get_post_type( $post_id )
                && 'auto-draft' != get_post_status( $post_id ) ) {
                    $show = get_post( $post_id );
                    if( 0 == $show->post_parent ){
                        $children =& get_children(
                            array(
                                'post_parent' => $post_id,
                                'post_type' => 'page'
                            )
                        );

                         if( empty( $children ) ){

                $child = array(
                                'post_type' => 'page',
                                'post_title'     => 'Title',
                                'post_name'      => 'page-title',
                                'post_date' => '2015-10-21 15:15:15',//[ Y-m-d H:i:s ]
                                'post_date_gmt' => '2015-10-21 15:15:15',//[ Y-m-d H:i:s ]
                                'post_content' => '',
                                'post_status' => 'publish',
                                'comment_status' => 'closed',
                                'post_parent' => $post_id,
                                'post_author' => 1,
                            );
                            $new_page_id = wp_insert_post( $child );
                            update_post_meta( $new_page_id, '_wp_page_template', 'page-template.php' );


                                }

                        }
                    }
                }
            }
            add_action( 'save_post', 'add_children' );