A custom walker can be passed to wp_list_pages() using the $walker parameter.
Here is a custom walker named WPSE_Walker_Page_Comment_Count() which is based on the default page walker, Walker_Page(). We’re only overriding the start_el() method in this case. The output has been customized to include the comment count.
First, add the walker code to your theme’s functions.php or to a plugin:
class WPSE_Walker_Page_Comment_Count extends Walker_Page {
// Copied from Walker_Page::start_el() core version v4.7.4.
/**
* Outputs the beginning of the current element in the tree.
*
* @see Walker::start_el()
* @since 2.1.0
* @access public
*
* @param string $output Used to append additional content. Passed by reference.
* @param WP_Post $page Page data object.
* @param int $depth Optional. Depth of page. Used for padding. Default 0.
* @param array $args Optional. Array of arguments. Default empty array.
* @param int $current_page Optional. Page ID. Default 0.
*/
public function start_el( &$output, $page, $depth = 0, $args = array(), $current_page = 0 ) {
if ( isset( $args['item_spacing'] ) && 'preserve' === $args['item_spacing'] ) {
$t = "\t";
$n = "\n";
} else {
$t="";
$n = '';
}
if ( $depth ) {
$indent = str_repeat( $t, $depth );
} else {
$indent="";
}
$css_class = array( 'page_item', 'page-item-' . $page->ID );
if ( isset( $args['pages_with_children'][ $page->ID ] ) ) {
$css_class[] = 'page_item_has_children';
}
if ( ! empty( $current_page ) ) {
$_current_page = get_post( $current_page );
if ( $_current_page && in_array( $page->ID, $_current_page->ancestors ) ) {
$css_class[] = 'current_page_ancestor';
}
if ( $page->ID == $current_page ) {
$css_class[] = 'current_page_item';
} elseif ( $_current_page && $page->ID == $_current_page->post_parent ) {
$css_class[] = 'current_page_parent';
}
} elseif ( $page->ID == get_option('page_for_posts') ) {
$css_class[] = 'current_page_parent';
}
/**
* Filters the list of CSS classes to include with each page item in the list.
*
* @since 2.8.0
*
* @see wp_list_pages()
*
* @param array $css_class An array of CSS classes to be applied
* to each list item.
* @param WP_Post $page Page data object.
* @param int $depth Depth of page, used for padding.
* @param array $args An array of arguments.
* @param int $current_page ID of the current page.
*/
$css_classes = implode( ' ', apply_filters( 'page_css_class', $css_class, $page, $depth, $args, $current_page ) );
if ( '' === $page->post_title ) {
/* translators: %d: ID of a post */
$page->post_title = sprintf( __( '#%d (no title)' ), $page->ID );
}
$args['link_before'] = empty( $args['link_before'] ) ? '' : $args['link_before'];
$args['link_after'] = empty( $args['link_after'] ) ? '' : $args['link_after'];
// Get the comment count for the page.
$comments_number = get_comments_number( $page->ID );
if ( 0 == $comments_number ) {
$comments_number_output = __( ' — No Repsonses', 'text_domain' );
} else {
$comments_number_output = sprintf(
/* translators: number of comments */
_nx(
' — %1$s Response',
' — %1$s Responses',
$comments_number,
'comments title',
'text_domain'
),
number_format_i18n( $comments_number )
);
}
$output .= $indent . sprintf(
'<li class="https://wordpress.stackexchange.com/questions/267058/%s"><a href="https://wordpress.stackexchange.com/questions/267058/%s">%s%s%s%s</a>',
$css_classes,
get_permalink( $page->ID ),
$args['link_before'],
/** This filter is documented in wp-includes/post-template.php */
apply_filters( 'the_title', $page->post_title, $page->ID ),
$args['link_after'],
sprintf( '<span class="comment-count">%s</span>', // Append comment count.
$comments_number_output
)
);
if ( ! empty( $args['show_date'] ) ) {
if ( 'modified' == $args['show_date'] ) {
$time = $page->post_modified;
} else {
$time = $page->post_date;
}
$date_format = empty( $args['date_format'] ) ? '' : $args['date_format'];
$output .= " " . mysql2date( $date_format, $time );
}
}
}
Then in your template, call wp_list_pages() like this:
<ul><?php
wp_list_pages( array(
'title_li' => '',
'depth' => 1,
'child_of' => get_the_ID(),
'sort_column' => 'post_title',
'show_date' => 'modified',
'date_format' => $date_format,
'walker' => new WPSE_Walker_Page_Comment_Count(),
) );
?></ul>
Note that I used get_the_ID(), which is cleaner than using the global $id variable. Also, $date_format was never defined in your original code. The most important part is the addition of the $walker parameter, which tells wp_list_pages() to use our custom walker to generate output.
Example output (formatted for legibility):
<ul>
<li class="page_item page-item-1090">
<a href="http://example.com/parent-page/child-page-01/">Child Page 01<span class="comment-count"> — 1 Response</span></a>
</li>
<li class="page_item page-item-1092">
<a href="http://example.com/parent-page/child-page-02/">Child Page 02<span class="comment-count"> — No Responses</span></a>
</li>
<li class="page_item page-item-1094 page_item_has_children">
<a href="http://example.com/parent-page/child-page-03/">Child Page 03<span class="comment-count"> — 2 Responses</span></a>
</li>
<li class="page_item page-item-1096">
<a href="http://example.com/parent-page/child-page-04/">Child Page 04<span class="comment-count"> — No Responses</span></a>
</li>
<li class="page_item page-item-1098">
<a href="http://example.com/parent-page/child-page-05/">Child Page 05<span class="comment-count"> — No Responses</span></a>
</li>
</ul>