Passing parent package configuration file to child packages

I have a Master parent package, which in turn executes 10 different child packages.

Currently, parent and child packages uses a configuration file which points to Sandbox server.

I want to point the parent package to QA environment now. In the SQL Agent job, while scheduling the parent package, I am passing the QA config file, but the settings from QA config files, does not get passed to the child packages.

How do I pass the parent package config file to child packages, even though they have their own config files??