I hadn't tried this because I was under the impression that the parent view would be disconnected from the scope when the child scope was active. Per the documentation on ion-nav-view:
By default, views are cached to improve performance. When a view is navigated away from, its
element is left in the DOM, and its scope is disconnected from the $watch cycle. When
navigating to a view that is already cached, its scope is then reconnected, and the existing
element that was left in the DOM becomes the active view. This also allows for the scroll
position of previous views to be maintained.
I'll give the emit/on a try and see what happens.