# How to create and use a WordPress child theme

> Editing a WordPress theme's files directly works, until the theme's next update: every customisation then disappears without warning. A child theme fixes this with just two files.

- Source canonique : [https://allaux.fr/en/guides/creer-theme-enfant-wordpress](https://allaux.fr/en/guides/creer-theme-enfant-wordpress)
- Langue : EN
- Dernière mise à jour : 2026-09-30

## Direct answer

> Create a new folder in wp-content/themes with a style.css file whose Template header points to the parent theme's folder, and a functions.php file that enqueues the parent's stylesheet. Then activate this child theme from Appearance, Themes.

## wp-content/themes/mon-theme-enfant/style.css

```
/*
 Theme Name: Mon Thème Enfant
 Template: nom-du-dossier-du-theme-parent
*/
```

## wp-content/themes/mon-theme-enfant/functions.php

```
add_action('wp_enqueue_scripts', function () {
    wp_enqueue_style('parent-style', get_template_directory_uri() . '/style.css');
});
```

## Creating the child theme

1. **Create a new theme folder** — In wp-content/themes, create a folder dedicated to the child theme, separate from the parent theme's folder, which must never be edited directly.
2. **Create the style.css file** — The file header needs a theme name and, crucially, the Template line, which must exactly match the parent theme's folder name, case-sensitive.
3. **Create the functions.php file** — This file needs to enqueue the parent's stylesheet before adding the child's own customisations, so the parent's styles always apply as a baseline.
4. **Activate the child theme** — From Appearance, Themes, the child theme appears as a fully installed theme and activates the same way as any regular theme.
5. **Add customisations progressively** — Any file from the parent theme can be copied into the child theme unchanged to be edited there; WordPress then automatically uses the child theme's version instead of the parent's.

## Why this mechanism protects customisations

When a child theme is active, WordPress first looks for each template file in the child theme's folder. If it isn't found there, it automatically falls back to the matching file in the parent theme. This means only the one file being changed needs to be copied into the child theme, rather than duplicating the entire parent theme.

When the parent theme is updated, only the files in the parent folder get replaced by the new version: the child theme's files stay untouched, since they live in a completely separate folder. That's what makes customisations survive updates, unlike a direct edit to the parent theme, which would be overwritten at every update.

## Common mistakes

- Copying every file from the parent theme into the child theme instead of only the ones actually being changed, which cancels out the benefit of the parent's future updates for everything else.
- Getting the folder name wrong on the Template line: a different case or an incorrect name stops WordPress from linking to the parent theme, and the child theme can't be activated.
- Forgetting to keep the parent theme installed: WordPress needs both themes present, since the parent is never activated directly but remains essential for the child to work.
- Trying to change a parent PHP function by redeclaring it identically in the child theme, which triggers a redeclaration error rather than a clean override.

## Child themes also apply to translations

> A child theme can include its own language files folder, loaded ahead of the parent theme's, which makes it possible to adapt some interface text without ever touching the parent theme's original files.

## FAQ

### Does a child theme slow down the site?

No, the overhead is negligible: WordPress simply checks whether the file exists in the child theme before loading the parent's, which has no measurable impact on performance.

### Can a child theme be created from any parent theme?

In theory, yes, for most standard themes, but some premium themes or ones built around a specific page builder document their own customisation method, worth checking before creating a standard child theme.

### Is a child theme needed even for small CSS tweaks?

For simple CSS adjustments, WordPress also offers additional CSS in the Customizer, without creating a child theme. A child theme becomes worthwhile once the customisation touches template files or PHP code.