Split a child theme's functions.php into included files

A functions.php that grows past a few hundred lines is hard to review. This pattern keeps it as a short loader that pulls in one file per feature, plus every file in a folder for things like custom post types and taxonomies.

Pick the Right Path Function

The most common bug in child themes is loading files from the wrong theme. Use the function that matches where the file lives:

In a child theme, get_template_directory() points at the parent, so files you add to the child theme won't be found.

Loader Pattern

Put this in the child theme's functions.php:

<?php
/**
 * Child theme loader.
 */

// Single feature files.
require_once get_stylesheet_directory() . '/inc/block-styles.php';
require_once get_stylesheet_directory() . '/inc/woocommerce.php';

// Every file in a folder (loaded in alphabetical order).
foreach ( [ 'post-types', 'taxonomies' ] as $folder ) {
	foreach ( glob( get_stylesheet_directory() . "/{$folder}/*.php" ) ?: [] as $file ) {
		require_once $file;
	}
}

With a layout like:

my-child-theme/
├── functions.php
├── style.css
├── inc/
│   ├── block-styles.php
│   └── woocommerce.php
├── post-types/
│   └── my-cpt.php
└── taxonomies/
    └── my-taxonomy.php

Notes:

• require_once avoids fatal "cannot redeclare" errors if a file is loaded twice.

• glob() returns false on some systems when it fails, so ?: [] keeps the loop safe.

• glob() sorts results alphabetically. If one file depends on another, prefix them (10-base.php, 20-extra.php).

• Each included file should register its own hooks (for example add_action( 'init', ... ) to register a post type) rather than running code immediately.

See Custom Post Type Admin for an example post type file.