Creating an insert update that will attach to the Child Object.

To attach to the Child Object please Create 2 insert updates.

Insert Update #1:
Type = Advanced.
Object name = Child Object.
Field- Value Pairs =  'Parent object Id' or 'Record Id'. = <<PARENTobject_id>>
"Run at Beginning" = Checked.
Save.

Insert Update #2:
Type = Advanced.
Object name = Child Object.
Field- Value Pairs =  'Object Id' or 'Record Id'. = <<CHILDobject_id>>
"Update existing record" = Checked
"Attach to the Object" = Checked.

Run DDP. Expected result = document attached to notes and attachments of the Child Record.