Hi, in my site there is two parent category (services and projects). Both has some child pages.
I'd like to do a grid that show the hages that have common sub-category
Welcome to our forum.
I am not sure if you are using pro version, there is an option to add custom query parameter where you can put custom post queries arguments, please see the screenshot of how you will get child pages on the post grid.
if you are using free version there is a filter hook for post grid query arguments you can do it via filter hook