Right after a morph A is added to a new owner morph B8, morph A is notified by a keyword message with argument the new owner.
Implement this method in your morph A class for posterior adjustments. For example, to center a child morph in its new owner:
noteNewOwner: morphB
self morphPosition: morphB morphExtent - self morphExtent // 2
Morph B is the parent morph presenting morph A in its boundaries. It can use all sort of strategies as automatic layout or hard-coded child position.