What Is A Child Theme and Why Do I Care?

[su_pullquote]In WordPress, a child theme is a theme that derives its functionality and style from another theme, called the parent theme.[/su_pullquote]

Child, Parent and Framework

Creating a Child theme is the WordPress industry-standard method of modifying an existing theme. If you’d like to customize a theme, especially a theme based on a framework (like Genesis, for example) the accepted approach is to use a child theme. A child theme is a separate theme and contains all of your specific customizations. The idea is that if the parent theme is ever updated (and WordPress is frequently), your modifications are not lost.
It is important to note that a theme framework is not an actual theme but rather a “drop-in” code library that is used to facilitate development of a Theme.
A theme framework is not a stand-alone theme and cannot operate independent of a theme. Its library of functions is included (bootstrapped) in a theme’s files to quickly boost design and functionality of the new theme. Twitter Bootstrap is a popular example of a “drop-in” code library.

Twitter Bootstrap is a popular theme framework. Sandbox, Thematic and WP Framework are other examples of theme frameworks. A stand-alone or base theme is a Theme that has all of the necessary files to run as a separate install. Such a theme can operate independent of a parent theme. The Twentyfifteen (currently the default) WordPress theme is an example of a stand-alone theme. It is a parent theme since child themes can be built upon it.

So why should I use child themes rather than modifying the parent theme?

1. Retain your custom modifications.
Wordpress is constantly being updated and improved. It is one of the most attractive features. However If you modify a theme directly you will lose your customizations when WordPress is updated. By using a child theme you will ensure that your modifications are preserved.
2. More easily track your work on a specific project
For developers a child theme, by keeping your changes separate, you can more easily track your work on a specific project.
3. Speed up development time on future projects.
4. Use of child themes is accepted industry practice.

Conclusion
As a professional developer, you should definitely follow industry standards (even if you are not, its a good practice). Creating child themes is an organized and productive way to use WordPress. If you’re still not convinced, consider this. One day you are going to ask a third party to fix a WordPress problem for you. Then you will have to hear: “Why didn’t you put your modifications in a child theme?”