Hi Tim,
A report request can only include data from a single AdWords account. To gather reporting data for all the accounts under your MCC account, you need to submit a separate report request for each account by setting the clientCustomerId header. The
ParallelReportDownload Java example shows how to download a report from an XML report definition for all accounts directly under a manager account in multiple parallel threads. This example should be run against an AdWords manager account. Example code in other languages is provided
here.
Regards,
Shwetha, AdWords API Team.