Display a list of child posts on parent posts of a custom post type

The best way is using WP_Query. I think your error or plugin error could be that the ‘post_type’ of childs is not define.

WP Query : https://codex.wordpress.org/Class_Reference/WP_Query

global $post;

$args = array(
    'post_parent' => $post->ID,
    'posts_per_page' => -1,
    'post_type' => 'products', //you can use also 'any'
    );

$the_query = new WP_Query( $args );
// The Loop
if ( $the_query->have_posts() ) :
while ( $the_query->have_posts() ) : $the_query->the_post();
  // Do Stuff
    the_title();
    echo "<br>";
    the_content();
endwhile;
endif;
// Reset Post Data
wp_reset_postdata();