Child Themer include custom function
<?php
// Include the front-end.php file only to non-admin pages.
if ( ! is_admin() )
include_once( get_stylesheet_directory() . '/custom/front-end.php' );
// Include the front-end.php file only to admin pages.
if ( is_admin() )
include_once( get_stylesheet_directory() . '/custom/back-end.php' );