我们可以通过映射category_name 查询变量（从pretty permalinks设置）到category__in （忽略子类别）：

function wpse_184127_ignore_category_children( $wp_query ) {
    if ( $wp_query->is_main_query() && $wp_query->is_category() && $name = $wp_query->get( \'category_name\' ) ) {
        if ( $term = get_term_by( \'slug\', sanitize_title_for_query( $name ), \'category\' ) ) {
            if ( $term->parent )
                $depth = count( get_ancestors( $term->term_id, \'category\', \'taxonomy\' ) );
            else
                $depth = 0;

            if ( $depth <= 1 ) {
                $wp_query->set( \'category__in\', array( $term->term_id ) );
                unset( $wp_query->query_vars[\'category_name\'] );
            }  
        }
    }
}

add_action( \'pre_get_posts\', \'wpse_184127_ignore_category_children\' );