Pipelines - Adding child data to Json Request using Webhooks Channel

Hello!  I have been using the Webhooks Channel in Pipelines to send data to a 3rd party app when a record is updated with the Make Request step and it works well.  However, now I need to send a data package that uses fields from a record in the parent table (Sales) and its related children (Line Items) in the same request such that the values from each related Line Item are included within an array in the body of the Json.

How can I get Pipelines to populate the array in the body of the Json request with data from the child records (the number of which can vary)?

------------------------------
Roger Dartnell
------------------------------