Exclude child term posts from parent term archive page

For the past weeks I’ve been searching for a solution to exclude child term posts on the parent term archive page. I’ve tried several solutions without success. Is there any best practice for this?

I found this code, but since my php skills are none existing I have not been able to solve the syntax errors this produces when I put it in my functions.php:

$parent_posts = get_posts(array(
    'tax_query' => array(
        array(
            'taxonomy' => $taxonomy,
            'field' => 'slug',
            'terms' => $parent_term,
            'include_children' => 0
        )
    ),
    'post_type' => $post_type
));

Any ideas?