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That shortcode will display all pages which have the page with the ID 936 set as their parent page.
There is no bug in the theme’s [blog] shortcode, I tested the above shortcode on my Mingle sandbox site and it works.
Your problem may be caused by the fact that there are curly “smart” quotes in the shortcode you have posted. Make sure all the quote characters in shortcodes are ordinary quote characters like this → "
This is one of the reasons why we tell you to follow the instructions on the forum home page if you want to include code in your posts such as shortcodes, HTML, CSS, JavaScript, PHP, and so on. I’ve told you to do this a dozen times or more now and if you can’t be arsed to do that, it’s your lookout. It ain’t rocket science to wrap your code in <pre> and </pre> tags.