Setting Stage Co-ordinates

How should I set the Co-ordinates of one object relative to another ?

Eg: Balloon, Monkey

If I need the Monkey co-ordinates fixed relative to the Balloon only and my Global or Stage Co-ordinates fixed at the Top - Left hand corner should not affect my Monkey’s movements.

i.e Monkey’s co-ordinates computed with respect to Balloon’s only.

Thank you.