How to apply custom post type template to child custom posts

I have created a custom post type called services in my WordPress installation. I have created single-services.php template. However, 2nd level posts aren’t picking up this template and I am not sure why.

Example posts in the service custom post type:

Cleaning (works as expected – using the single-services.php template)

–Deep cleaning (a child of ‘cleaning’ post above, reverts to the next template in the template hierarchy, in my case the index.php)

I would like all my services posts to use the same template, i.e. single-services.php template.

Any help is appreciated.

Thanks