'father', 'son' and 'grandson'

I’ve built a simple diagram with a sub-graph within a subgraph. The hierarchy is of 3 levels: ‘father’, ‘son’ and ‘grandson’.
When I drag the ‘father’ - only the ‘son’ moves with it, and when I drag the ‘son’ - the ‘grandson’ moves.
What do I need to do for the ‘grandson’ to move when dragging the ‘father’?

Really? That is not the normal behavior. You can try this, for example, in the Grouping sample of the GoWpfDemo.