[as2] Collision Detection

Hi.
I´d like to know how can I make a collision detection between two objects with complex shapes.
Each object has a child movieclip.
Example:

obj1.child
obj2.child

I need to make a collision detection test between each child of those two objects.

As far as I know. I can use the hitTest for bitmap. But isn´t working.
I´m not finding the right way to do it.
I think it needs localToGlobal for x and y for each child clip coordinates and matrix, because obj1.child and obj2 rotates on _root.onEnterFrame.

Anybody know how?

Thanks