Get Child Page IDs by Parent ID

Question

I am currently trying to grab a child page id from a custom post type, but my values returned are always null. I know that the particular ID I'm passing has a parent so there should be a match.

What is the appropriate way to grab child ids using the parent id?

This is what I have tried:

$parentid = $order->get_id();

$args = array(
  'post_parent'     => $parentid,
  'post_type'       => 'shop_subscription'
);

$child = new WP_Query($args);

if ($child->have_posts()) : while ($child->have_posts()) : $child->the_post();
  $childid = get_the_id();  
endwhile;
else:
  $childid = "not set";
endif;

Answer 1

This should work. I'm not entirely sure what is wrong with your code (it's getting late) but the below code works on my end. Obviously I replaced $order->get_id() with a known ID and post_type was set to page.

<?php 
    $parentid = $order->get_id();

    $child = new WP_Query( array('post_parent' => $parentid, 'post_type' => 'shop_subscription') );

    if ($child->have_posts()) : while ($child->have_posts()) : $child->the_post();
        $childid = get_the_ID();
    endwhile;
        else:
            $childid = "not set";
    endif;

    wp_reset_query();

?>