Show the excerpt instead of content

<ul class="thumbnails">
   <?php
   $mypages = get_pages( array( 'child_of' => $post->ID, 'sort_column' => 'post_date', 'sort_order' => 'desc' ) );

    foreach( $mypages as $page ) {
       $content = $page->post_content;
          if ( ! $content ) // Check for empty page
           continue;

  $content = apply_filters( 'the_content', $content ); ?>

<li class="span4">

    <article class="thumbnail clearfix">

   <h3><a href="<?php echo get_page_link( $page->ID ); ?>"><?php echo $page->post_title; ?></a></h3>

        <p><?php echo $content; ?></p> 

   <a href="<?php echo get_page_link( $page->ID ); ?>" class="btn btn-primary pull-right">Read More</a>

    </article>
</li>
              <?php
                          	}
                          ?>
</ul>

Im using this function http://codex.wordpress.org/Function_Reference/get_pages#Displaying_Child_pages_of_the_current_page_in_post_format

This shows me the whole content, I only want the excerpt.

I tried the echo $excerpt and the_excerpt with no success.
Anybody know the solution? Thanks