我不完全确定我是否正确地理解了你的问题，因为“这不是一个可选的部分”，但是。。。

您将获得ID为2的页面的子页面，因此看起来您希望显示该页面的标题。如果是这样，那么此代码将解决您的问题：

<?php
    $args = array(
        \'post_type\'      => \'page\', //write slug of post type
        \'posts_per_page\' => -1,
        \'post_parent\'    => \'2\', //place here id of your parent page
        \'order\'          => \'ASC\',
        \'orderby\'        => \'menu_order\'
    );

    $childrens = new WP_Query( $args );

    if ( $childrens->have_posts() ) :
?>
    <div class="content">
        <h2 class="big grid_3"><?php echo get_the_title(2); ?></h2>
        <div class="grid_6 right">
            <?php while ( $childrens->have_posts() ) : $childrens->the_post(); ?>
            <div class="grid_2 left" id="teaser" >
                <p class="subtitle"></p>
                <h3><?php the_title(); ?></h3>
                <?php the_excerpt(); ?>
                <a class="cta_light" href="<?php the_permalink(); ?>">Mehr erfahren</a>
            </div>
            <?php endwhile; // <- I had to move that, it was in wrong place so you were closing more divs than you were opening in that loop ?>
        </div>
    </div><!-- .content -->
<?php
    endif; 
    // wp_reset_query();  <- there is no point in resetting query - you haven\'t changed it
    wp_reset_postdata(); // on the other hand you should reset postdata
?>