Sychronising MCs

I have two MultiFramed MovieClips
In a parent - child setup
With the child being in the timeline of the parent.

The Parent is added to the stage via addChild() . And for a sprite effect is accessed through gotoAndStop()

I wish for both movieclips to be synchronised in there frame position.

Yes I can add to everyone of the parent’s frames an action eg instance.gotoAndStop(currentframe).
However all those stubs of code seem silly,
What’s the best way to do this via a3 code??