custom-functions14.php

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