Unable to delete related media attachments with deleted post

I want to delete the post attachments too from the 'Media panel once a custom post is deleted. The post itself gets deleted well, but its media still remains in the wordpress media panel:

Archive page:

?php

if (isset($_POST['delete-btn'])) {

    $deletePost = $_POST['post-id'];

    wp_delete_post( $deletePost, true);
    do_action( 'delete_post', $_POST['post-id'] );
}
?

Functions.php:

//delete all media attached with deleted post
    add_action( 'delete_post', 'delete_post_children' );

    function delete_post_children( $post_id )
    {
    wp_delete_attachment( $post_id );
};
//delete all media attached with deleted post end

Please help. Thanks.