Get child post ID’S

Greetings,

My customer has requested to not show syndicate posts in the main loop but to display them elsewhere.

I was wondering if there was a way to easily get the post ID’s that have a parent so I can filter them out?

I did manage to accomplish it using $wpdb however, I was wondering if there was already a better built in way? I wasn’t able to find anything regarding this.

Current Code(I realize it may be nasty it’s just for testing purposes):

add_action('pre_get_posts','alter_query');
function alter_query($query) {
    global $wp_query, $wpdb, $synposts;
    
    $blog_id = get_current_blog_id();
    $db = $wpdb->base_prefix . '_3wp_broadcast_broadcastdata';
    $syndicatePosts = array();
    
    $syndicateDB = $wpdb->get_results(
    "
       SELECT post_id, data
       FROM $db
       WHERE blog_id = $blog_id
    "
    );
    foreach($syndicateDB as $syn_post){
        $syn_data = unserialize(base64_decode($syn_post->data));
        if(isset($syn_data['linked_parent'])){
            $syndicatePosts[] = $syn_post->post_id; 
        }
    }
    $synposts = $syndicatePosts;

	if ( !$query->is_main_query() )
		return;
 
	$query-> set('post__not_in' , $synposts );
 
} 

Thank you for your time.