When delete parent node, how to delete children or unpublish them or not display children in a view

I am using a calendar view to display the children nodes (with date fields) of various relationships. Now, a user deleted a parent node, but I'm still showing the children nodes on the calendar.

I thought I could just modify the view to ignore children nodes without parents, but I couldn't figure out a way to do that in D5.

I thought I could use actions (When a content type is deleted) and triggers (delete or unpublish the children), but I could not figure out a way to create the trigger action.

Anyone encounter anything like this?