I had to try this out, so I added the code to one of my themes and tried it out...long story short, this is a very cool option to add to themes. I know there are a lot of people who are new to WordPress, especially theme modifications, let alone creating a child theme (which can be challenging). Normally with my premium themes I include a premade child theme, but for the free versions, we cannot add child themes to the install package.

On my first try, I clicked on activate child theme and sure enough it literally created a child theme and activated it at the same time. One thing I did was modify the screenshot path for copying a custom child theme screenshot located in the parent theme's image folder....it worked!

There is one item of thought that would be an awesome addon would be to import the parent theme Customizer options should a user already have settings already set like colours, blog style, etc.

Overall, this is a very nice function to offer newbies by simply clicking on a link to create and activate a child theme.