There was an issue with the first release of this theme that meant child themes were not working.
You can now download a sample child theme for this theme which works with the latest version of the theme.
The parent theme was built with SASS and also uses php-sass to inject styles based on theme options. In a child theme we may want to replace styles so the sample child theme loads these in a way that allows full control. See functions.php and style.css in the child theme.