As you have not mentioned where the 'targetObj' is located, I'll take a guess that you are probably talking about a movieclip instance in the flash stage.
If you have other classes (.as files) and want to allow them to have access to the big family (of you sprites & MC's) then you may :
- Initialize them in document class
- Have them inherit document class
- Have movieClips extended with a base class
In short you will have to link the document class to other classes to be able to access classes in the flash IDE or the stage itself, as document class is the entry point to all you custom classes.