Is it possible to add test Test Plan or Test suite or Test case (RQM) as a child for work item type "Task" in CCM?

I don't believe that this is supported, given the particulars of the master/child relationship, but I'll see if I can find someone who can answer this better than me. You certainly can link artifacts across CLM applications, as described in this help topic.

Hi Pravin,

link types are used to describe the link between artifacts. For example, a test case tests a plan work-item. A plan work-item is tested by a test case. These link types are used to provide interesting queries such as “All plan items with failing test cases”. You could refer to this great jazz.net blog (and associated short video) located here: "Sprint alignment for developers and testers". It was created for RTC/RQM 2.0 but it's still applicable for CLM 2012.

I wonder what is your business case here.
I'm unsure about the semantics of having a Story to be a parent of a Test Case, a Test Suite or a Test Plan.

If you're a test lead who wants to assign work to test team members (e.g. creation of test cases, test environments, etc.),  I'd recommend creating Task-Quality Work-item in RQM instead. This will result in the creation a WI in RTC (possibly a Story, depending on your choice) but note that it will not derive in a parent/child relationship.

Wrt the direct linking from a RTC Task, you will find the following options:  
- "Related Test Case"
- "Related Test Plan"  --> note: this is typically the kind of link you'll get when creating a Quality-Task WI from the "Test Cases" section of a Test Plan in RQM
- "Tested by Test Case"
or simply
- "Related Artifacts" (generic linking)

Regards,
Stéphane