Help creating bootstrap3 child theme for OJS3.1.2

I’m trying to learn how to create a child theme with the Bootstrap 3 theme as its parent, but my study of the documentation doesn’t seem to be helping me to understand some of the basics. My understanding was that a basic, minimal child theme should behave exactly like its parent, but when I try to use a child theme that merely sets bootstrapthreethemeplugin as its parent I end up with pages that are badly mangled.

Starting with a bare minimum bootstrap 3 child seemed like a good way to get started learning and building new themes with the potential for incorporating bootstrap’s design elements. Can anyone offer help or advice with this first step?

To put this more directly:

The theming guide’s discussion of child theme’s for Bootstrap 3 says that you only need to create a LESS file with variables you choose to override in the parent theme and this code:

 * Load the custom styles for our theme
 * @return null
public function init() {
    $this->modifyStyle('bootstrap', array('addLess' => array('styles/variables.less')));

That’s exactly what I’ve done in the code posted in the previous comment, but the theme is thoroughly broken. Is the theming guide leaving out a crucial step, or have I missed something?