Windows State Machine workflow: How can we achieve Parent Child workflow communication when both are hosted as WF service

I am trying to spawn child workflows as services from parent workflow which is also a workflow hosted as a service.

Problems I am facing:

1. How to spawn multiple child workflows开发者_JAVA技巧 as service "synchronously"?
2. How to communicate to the consuming applications that the child workflows are ready for action?
3. How to communicate to the parent that a child workflow is complete "synchronously"?