In a n-tier approach, object-oriented or "unbound-mode", what's the best way to code the deletion of child data in parent-child relationships before/after changes are confirmed?

If I use a collection object to represent the child data, do I need to keep another collection object to keep track of deleted items in order that if the user saves the changes I know which I actually have to delete or should I just use the original collection object with perhaps a property that "flags" the deletion?

Am I making sense?