Profile: Farrel

Problem:
Retrieving multiple child post IDs based on parent post ID using post relationship API

Solution:
You should use the Post Relationship API function toolset_get_related_posts in this case to retrieve all related posts.

You can find proposed solution, in this case, with the following reply:
=> https://toolset.com/forums/topic/retrieving-multiple-child-post-ids/#post-1079482

Relevant Documentation:
=> https://toolset.com/documentation/customizing-sites-using-php/post-relationships-api/#toolset_get_related_posts