exclude children posts from parent taxonomy term page

exclude_children.php

function exclude_children($wp_query) {
    if (isset($wp_query->query_vars['tax_name'])) {
        $wp_query->set('tax_query', array(array(
            'taxonomy' => 'tax_name',
            'field' => 'slug',
            'terms' => $wp_query->query_vars['tax_name'],
            'include_children' => false
        )));
    }
}  
add_filter('pre_get_posts', 'exclude_children');