The Task Parallel Library in the .NET Framework 4 provides an opt-in feature that enables parent-child relationships between tasks.  This relationship brings with it some additional behaviors, including that a parent task is not considered completed until all of its child tasks have completed, and that exceptions from any faulted child tasks are bubbled up to the parent. The relationship is also visible through the new Parallel Tasks window in Visual Studio 2010.  That's a very cursory description of what's actually a rich topic with several subleties: if you would like to understand better parent-child relationships between tasks in .NET 4, read this in-depth paper written by Ling Wo and Cristina Manu:

Parent-Child Task Relationships in the .NET Framework 4

(This paper and many more are available through the Parallel Computing Developer Center on MSDN at http://msdn.microsoft.com/en-us/concurrency/ee851578.aspx.)