Nested movie clips and mouse click

i have three movie clips A and B and C ( B and C are inside A ). A is on stage. Now when i click anywhere on stage, how do i check if i am clicking outside A or on B or C ?? …
if regestration point of B and C is same, how do i get relative co-ordinates of mouse from that point ???
(plz help with usage of localToglobal in this case)