Never mind about my question… here is your answer
Put this function on your functions.php
// Get Featured Image Path
function get_featured_image_link($size){
global $post;
$get_featured_image_link = get_the_post_thumbnail($post->ID, $size);
preg_match("/(?<=src=['|\"])[^'|\"]*?(?=['|\"])/i", $get_featured_image_link, $thePath);
return $get_featured_image_link_final = $thePath[0];
}
Then this is the process to get the image…
<?php
$the_query = new WP_Query(
array(
'post_parent' => '20',
'post_type' => 'page',
'sort_column' => 'menu_order'
)
); ?>
<?php while ( $the_query->have_posts() ) : $the_query->the_post(); ?>
<li id="<?php echo $page->post_name; ?>">
<h2><a href="https://wordpress.stackexchange.com/questions/34540/<?php the_permalink() ?>"><?php the_title(); ?></a></h2>
<img src="<?php echo get_featured_image_link('Path'); ?>">
</li>
<?php endwhile; ?>
<?php wp_reset_query() ?>
Set the width and height to whatever you want to…
Tested and worked!
Have fun!