Single parent post lists child posts with pagination

Something like this should do the trick for ordering by title, and using pagination:

    global $wp_rewrite, $wp_query;
    if ( have_posts() ) : while ( have_posts() ) : the_post();  ?>

    <header class="entry-header">
        <h1 class="entry-title"><?php the_title(); ?></h1>
    </header><!-- .entry-header -->

    <?php   //If top level, find children
        if($post->post_parent == 0):
            $children = new WP_Query(array(
                'post_type'=>'page',
                'post_parent'=>$post->ID,
                'paged' => $paged,
                'posts_per_page' => 20,
                'orderby' => 'title',
                'order' => ASC
            ));

            if($children->have_posts()): ?>
                <ul>
                <?php while ( $children->have_posts() ) : $children->the_post(); ?>
                    <li> <?php the_title();?> </li>
                <?php endwhile; ?>
                </ul>

                $wp_query->query_vars['paged'] > 1 ? $current = $wp_query->query_vars['paged'] : $current = 1;

                $pagination = array(
                    'base' => @add_query_arg('paged','%#%'),
                    'total' => $wp_query->max_num_pages,
                    'current' => $current
                );

                if( $wp_rewrite->using_permalinks() )
                    $pagination['base'] = user_trailingslashit( trailingslashit( remove_query_arg( 's', get_pagenum_link( 1 ) ) ) . 'page/%#%/', 'paged' );

                if( !empty($wp_query->query_vars['s']) )
                    $pagination['add_args'] = array( 's' => get_query_var( 's' ) ); ?>

                <?php echo paginate_links( $pagination ); ?>

            <?php else: ?>
                <?php echo 'No children';?>
            <?php endif; ?>

            <?php wp_reset_postdata(); ?>
        <?php else://Not top level, display normal post ?>
            <?php the_content(); ?>
        <?php endif;?>

    <?php endwhile; // end of the loop. ?>
<?php endif; ?>

You can move the paginate_links function to wherever you want the pagination to go.

As for displaying the total number of entries, you can use the $wp_query variable inside of the loop.

<?php echo $wp_query->found_posts; ?>