A Child Theme in WordPress is simply a “style only” Theme, and is easily made by adding Template: themefolder to your style’s header.
The basics of creating a Child Theme
If you want to create a Child Theme to Basic2Col your style.css header will turn out:

/*
Theme Name: My theme
Theme URI: http://mysite.tld/
Description: My Basic2col Child Theme
Version: 1.0
Author: Me
Author [...]