WordPress Child Themes: Why & How

A child theme is a small theme that inherits all templates, styles and features from an installed parent theme and overrides only what you add, so parent theme updates never erase your customisations. WordPress replaces the parent's folder on every update; edits kept in the child's separate folder are left alone.

• Update-safe: parent updates apply without losing your work.
• Separated: your code stays apart from the vendor's code.
• Minimal: you write only the files you actually change.

For a few colour or spacing tweaks, Additional CSS in the Customizer (classic themes) or Styles in the Site Editor (block themes) is enough. A child theme is for template edits, new functions and anything you would hate to lose.

In the child's functions.php, hook wp_enqueue_scripts, enqueue the parent's stylesheet with get_template_directory_uri(), then the child's with get_stylesheet_uri() listed as dependent on the parent.

<?php
add_action( 'wp_enqueue_scripts', 'astra_child_enqueue_styles' );
function astra_child_enqueue_styles() {
    wp_enqueue_style(
        'astra-parent-style',
        get_template_directory_uri() . '/style.css'
    );
    wp_enqueue_style(
        'astra-child-style',
        get_stylesheet_uri(),
        array( 'astra-parent-style' ),
        wp_get_theme()->get( 'Version' )
    );
}

• Avoid @import in style.css; it forces stylesheets to load one after another and slows the page.
• Check the parent first: some parents already load their CSS from other files, in which case you only enqueue the child stylesheet.
• Never copy parent functions: both functions.php files run (the child's first), so a duplicated function name causes a fatal error.

Copy the template file from the parent into the child at the same relative path — header.php, single.php, footer.php — and edit the copy; WordPress checks the child first, so the copy wins.

New templates, such as a custom landing-page layout or a template for a custom post type, also belong in the child. Change one file at a time and test in a private window; an incomplete copy can blank the page until restored. After major parent updates, compare your overrides with the new parent files, because fixes in the parent template do not flow into your copy. When something breaks, the WordPress 500 error guide shows how to find the failing file.

Yes: the free Child Theme Configurator plugin generates a child from Tools › Child Themes, and several theme vendors publish ready-made child themes or generators. Take a full backup first.

For changes that should survive switching themes altogether — a custom post type, a shortcode, tracking code — use a small plugin or a code-snippets plugin instead, because theme-attached code disappears when the theme changes. Teams without a developer often hand this layer to WebJi®'s WordPress web design service. The difference between theme and plugin responsibilities is set out in WordPress theme vs plugin.