how can i display children of my parent page in one of the children page (wordpress)

if you want to display all child pages of parent page in the child page then you can try this. it will display child page title and its links.

$current_page_id = get_the_id();
    $parent_id = wp_get_post_parent_id( $current_page_id );
    if(!empty($parent_id))
    {
        $child_args = array(
            'post_type'      => 'page',
            'posts_per_page' => -1,
            'post_parent'    => $parent_id,
            'post_status'    => 'publish',
            'order'          => 'ASC',
            'orderby'        => 'menu_order'
             );
        $parent = new WP_Query( $child_args );

        if ( $parent->have_posts() ) : 
        echo '<div class="single-sidebar">';
        echo '<ul>';
             while ( $parent->have_posts() ) : $parent->the_post();
                $addclass  = "";
                if($current_page_id == get_the_ID())
                {
                    $addclass  = "active";
                }
              ?>                        
                <li class="<?php echo $addclass; ?>"><a href="https://wordpress.stackexchange.com/questions/340859/<?php the_permalink(); ?>" title="<?php the_title(); ?>"><?php the_title(); ?></a></li>
                <?php 
            endwhile; 

            echo '</ul>';
            echo '</div>';
         endif; 
            wp_reset_postdata(); 
    }

let me know if this helps you