What Is a WordPress Child Theme? A Plain-English Guide

Almost every WordPress guide eventually tells you to use a child theme before you change anything. It sounds like extra work for a small tweak, so plenty of people skip it, and then lose their changes the next time the theme updates.

I've read through the official WordPress Theme Handbook on child themes so you don't have to. Here's what a child theme is, why the advice exists and what's involved in making one, explained without assuming you're a developer.

WordPress child theme meaning in plain English

The handbook describes a child theme as a theme that extends a parent theme. It inherits the parent's design and functionality, and you use it to customise the parent without editing the parent's own files.

Here's a way to picture it. Imagine renting a furnished flat. You can paint the walls and add your own pictures, but you'd rather not knock through the walls, because the landlord might refurbish and wipe out your work. A child theme is your own layer of paint and pictures, sitting on top of the building the parent theme provides.

Why people use a child theme in WordPress

The Theme Handbook gives a short list of reasons:

• Your customisations stay separate from the parent theme, so they're easy to reuse.
• You keep your changes when the parent theme is updated.
• You write only the code you need, which saves development time.
• It's a good way to begin learning theme development.

The update point is the big one. The handbook says changes in a child theme survive a parent update, while code added directly to the parent theme's functions file is lost when the parent updates.

What a child theme inherits and what it overrides

A child theme doesn't copy the parent. It starts empty and only needs the files you want to change. WordPress loads the parent for everything you haven't replaced.

• Template files: if the child has a file with the same name as one in the parent, the child's version is used.
• Template parts and patterns: these also override the parent's files of the same name, and patterns must share the same registered slug.
• The functions file: this one behaves differently. Both the parent's and the child's functions files load, with the child's loaded first. The child's file doesn't replace the parent's.

That last rule has a practical warning attached. The handbook says not to copy code from the parent's functions file into the child's, because duplicate function names cause fatal errors.

What goes in a child theme folder

At its simplest, a child theme needs just a folder and one stylesheet. The handbook walks through the steps using a default WordPress theme as the parent:

1. Create a folder in the themes directory of your WordPress install, using a lowercase name with hyphens between words.
2. Inside it, create a stylesheet file named style.css with a header comment at the top.
3. In that header, include a Template field whose value exactly matches the parent theme's folder name. This field is what marks it as a child theme.
4. Zip the folder and upload it under Appearance, then Themes, then Add New, and activate it.

The Template line is the part people get wrong. If the folder name doesn't match the parent's folder exactly, WordPress can't link the two, and the child theme won't work.

Loading your child theme's styles

Having a stylesheet isn't always enough to make it apply. How you load the styles depends on how the parent theme works, and the handbook sets out three situations:

If the parent theme...	What you need to do
Doesn't load its own stylesheet	Enqueue the child's stylesheet using the WordPress function for adding styles, on the standard scripts hook
Loads only the active theme's stylesheet	You may also need to enqueue the parent's stylesheet
Already loads both stylesheets	No extra enqueueing is needed

Enqueueing is WordPress's way of loading a stylesheet or script in an orderly fashion. It lives in the functions file, which is one reason that file matters in a child theme. The handbook also says to use its theme file path and URI functions, not hard-coded addresses, when your child theme refers to its own files.

WordPress child theme limits to know about

Child themes aren't the answer to every customisation job. The handbook is upfront about three limits:

• WordPress only supports two levels, parent and child. Grandchild themes aren't a standard option.
• Heavy customisation can become hard to maintain. In that case, the handbook suggests forking the parent into a full theme may be the better choice.
• Block themes add a user customisation layer, but the handbook says it's stored in the database, not in the filesystem.

A child theme also needs its own text domain, and the handbook says it should load its translations using the dedicated child theme function.

Child themes and WordPress Multisite networks

If you manage more than one site, there's an extra reason to care. On a network, themes are installed network-wide, so editing one changes it for every site using it, according to the Multisite documentation. A child theme lets one site be different without touching the shared parent. I've covered the way those networks are organised in what WordPress Multisite is.

Sharing your WordPress theme knowledge

Theme customisation is a topic many site owners struggle with, and clear write-ups are always in demand. If you've got a good way of explaining it, you might consider publishing it.

If you build WordPress sites, here are WordPress publications open to outside writers.

Frequently asked questions

Do I need a child theme for every WordPress site?

No. The handbook recommends one when you want to customise a parent theme without editing its files. If you're not changing the theme's code or templates, you may not need one.

Will a child theme survive a parent theme update?

Yes. The Theme Handbook says changes made in the child theme are kept when the parent updates, while code added directly to the parent's functions file is lost.

What makes a theme a child theme?

The Template field in the style.css header. Its value has to match the parent theme's folder name exactly.

Can a child theme have its own child theme?

Not as a standard option. The handbook says WordPress supports only two levels, parent and child.

Does the child theme's functions file replace the parent's?

No. Both load, with the child's loaded first, so you add to the parent's functions instead of replacing them.