pages plus subpages conditional tag

Hi, I created various template_parts which are recalled by page name.
The code is like this:

<?php get_template_part( $slug, $name );
if ( is_page( 'page_one' ) ) :
	get_template_part( 'media-page_one' );
elseif ( is_page( 'page_two' ) ) :
	get_template_part( 'media-page_two' );
else :
  get_template_part('');
endif
?>

How can I change this code so even the child pages get included?
I tried:

if ( is_page( 'page_one' ) || 'page_one' == $parent_name ) :
	get_template_part( 'media-page_one' );

…bur it doesn’t work. What am I missing?

thanks for any hint

Alby