trying to use callfunc in a useful way

I have the typical 1 screen, 1 scene setup. i.e. 1 screen owns many group ("scene") children.

Like this
SCREEN (main.brs)
  MAINSCENE (mainscene.xml/mainscene.brs)
       CHILD1
       CHILD2

Now, I expose interface functions on MAINSCENE "test". I would very much like to be able to callfunc on them.

It tired doing this in mainscene.brs
m.global.AddFields({utils:m});
then in CHILD1
m.global.utils.callFunc("test","hello world")

but this doesn't work... 

does anyone have a solution to this? From my reading, and seeing some other posts, I expected this to work.