Twenty Thirteen uses the following in functions.php:
require( get_template_directory() . '/inc/custom-header.php' );. When I copy /inc/custom-header.php to twentythirteen-child, it isn’t replaced. I can’t use
require() because two copies will be included. How this should be handled?
get_template_directory looks in the parent theme for files.
In the case a child theme is being used, the absolute path to the
parent theme directory will be returned. Use
get_stylesheet_directory() to get the absolute path to the child theme
This file is not meant to be replaced. You will need to find another way to do what you need to do.
Perhaps remove the function hooked here and add your own?