Okay, I think I got it all done. Can you test? First, add some Days, Sessions, and Breaks to the second day. Then test on one of the days. If something goes wrong, stop there.
1. First, delete a Break. Okay?
2. If okay, delete a Day. Okay? Were all the Sessions and Breaks for that Day also deleted?
3. If okay and yes, delete an Event. Were all the Days, Sessions, and Breaks deleted for that Day?