The advanced post selection adds the ability to query posts by a post parent. This options is a multi select field so you can add multiple post parents to query your posts.
Step 1: Open the post query section in the settings.
Step 2: Under “Include By” select “Post Parent” and “Select Posts Parents”will show up.
Step 3: In the “Select Posts Parents” field add your post parents that you want to show up in your posts query.