If you want to make use of all the nifty filters for the title and excerpt/content (and why would you not want that?) you should loop through a custom query instead of using get_pages
and the pages’ plain contents:
<?php
$args = array(
'post_type' => 'page',
'post_status' => 'publish',
'posts_per_page' => -1,
'post_parent' => $post->ID,
);
$query = new WP_Query($args);
while ($query->have_posts()) {
$query->the_post();
?>
<h2><a href="https://wordpress.stackexchange.com/questions/136190/<?php the_permalink(); ?>"><?php the_title(); ?></a></h2>
<?php
the_excerpt();
}
wp_reset_postdata();
?>