Childpage title + content on Parent Page

You rarely ever need a custom SQL query, use the tools WordPress has to offer:

$query = new WP_Query(
    array(
        'posts_per_page' => -1,
        'post_parent' => $post->ID,
        'post_type' => 'page',
        'orderby' => 'menu_order post_title',
        'order' => 'ASC',
    )
);

if ( $query->have_posts() ) : ?>

    <?php while ( $query->have_posts() ) : $query->the_post() ?>

        <div id="page-<?php the_ID() ?>">
            <?php the_content() // Use any template tags as you would normally ?>       
        </div>

    <?php endwhile ?>

    <?php wp_reset_postdata() // Restore the current page ?>

<?php endif ?>