The DeCouple addon is
really simple but useful: the selected parent object will be decoupled
temporarily from its children so youll be able to reposition the parent
without influencing
the children.
Documentation
First go to User Preferences->Addons and enable the DeCouple addon in the
Object category.
Select the parent object of your choice and invoke the addon (button in the
Object Tools panel).
If you wish to hotkey DeCouple:
In the Input section of User Preferences at the bottom of the 3D View >
Object Mode section click 'Add New' button.
In the Operator Identifier box put 'object.decouple'.
Assign a hotkey.
Save as Default (Optional).