Profile: larryB-3

Problem:
Display child posts of specific parent "location" posts

Solution:
Types plugin is using a hidden custom field _wpcf_belongs_[parent-slug]_id to store the parent post ID, for example, the custom post type "LOCATION" is using slug "location", then the custom field slug is "_wpcf_belongs_location_id". you can try this:
1) Dashboard-> Views-> Settings-> Features
in option "Hidden custom fields", find and enable the option "_wpcf_belongs_location_id"

2) Edit your view which list child "ART" posts, add a filter:
Select items with field:
_wpcf_belongs_location_id is a number in VIEW_PARAM(locationid)

3) put the Views's shortcode into your content, like this:
[wpv-view name="my-view-name" locationid="123,456"]
Please replace the 123, 456 with the post ID of LOCATION A and LOCATION C

Relevant Documentation: