Need Help! Do this if child page of a Page

I am trying to test for the child of a page. I have tried using this function found on the internet

function is_child($pageID) {
	global $post;
	if( is_page() && ($post->post_parent==$pageID) ) {
               return true;
	} else {
               return false;
	}
}

in the functions.php file …but to no avail.
My problem is simple; if the page is a child of another page, do this, elseif, etc..
I have this conditional statement in my header.php so that when any child of a main page is clicked on, the submenu under the main “Image/Title” area stays consistent. Here’s the code:

<?php if (is_page(13) || is_child(13) ) : ?>

<div class="subMenuContainer">
<?php	wp_nav_menu( array( 'items_wrap' => '%3$s', 'container_class' => 'subMenu', 'after' => '<li class="menu-divider">|',  'theme_location' => 'sectors' ) ); ?>
</div><!-- end subMenuContainer -->

<?php  elseif ( is_page(11) ||  is_child(11) ) : ?>

<div class="subMenuContainer">
<?php	wp_nav_menu( array( 'items_wrap' => '%3$s', 'container_class' => 'subMenu', 'after' => '<li class="menu-divider">|', 'theme_location' => 'services' ) ); ?>
</div><!-- end subMenuContainer -->

<?php  elseif ( is_page(17) ||  is_child(17) ) : ?>

<div class="subMenuContainer">
<?php	wp_nav_menu( array( 'items_wrap' => '%3$s', 'container_class' => 'subMenu', 'after' => '<li class="menu-divider">|',  'theme_location' => 'mediacenter' ) ); ?>
</div><!-- end subMenuContainer -->

<?php endif; ?>

Any help on this would be most appreciated. I have tried and tried different approaches but nothing is working
Refer to this site: http://ahminc.com/ahm/services/