How to display thumbnail + tags + title of a child page?

Assuming that you’ve enabled support for both post thumbnails and post tags for static Pages, I would use WP_Query() to build your query, and do something like the following:

global $post;
$child_pages_query_args = array(
    'post_type'   => 'page',
    'post_parent' => $post->ID,
    'orderby'     => 'menu_order'
);

$child_pages = new WP_Query( $child_pages_query_args );

if ( $child_pages->have_posts() ) : while ( $child_pages->have_posts() ) : $child_pages->the_post();
    ?>
    <div class="child-thumb">
        <a href="https://wordpress.stackexchange.com/questions/54394/<?php the_permalink(); ?>"><?php the_post_thumbnail(); ?></a>
        <a href="https://wordpress.stackexchange.com/questions/54394/<?php the_permalink(); ?>"><?php the_title(); ?></a>
        <?php the_tags(); ?>
    </div>
    <?php
endwhile; endif;

// Be kind; rewind
wp_reset_postdata();

Note that I’ve not included any failsafes, such as checking for has_post_thumbnail(), etc.