Updated Album Question - Parent and Sub-album

To show when a sub-album was last updated, I have successfully edited my themes/carbon/templates/local/album.tpl by adding the following code to Line item 193 (towards the bottom):

{if $child.canContainChildren}{g->text text="Updated: "}{$child.modificationTimestamp|date_format}{/if}"

My album structure is like this: Parent Album--->Sub-album 1--->Sub-album 2--->Actual photo items.

When I add new photos to Sub-album 2, Sub-album 2 correctly shows the updated date, but Sub-album 1 and the Parent Album do not also show the updated date.

When I add new photo items, how do I get Sub-album 1 and the Parent Album to reflect the same updated date as Sub-album 2?

Thanks in advance!