I'd like to add +1 to this feature and also suggest how it works:
They appear as a dropdown on the main page, accessible by an "expand" button in the "parent" delivery, and are displayed as an indented list. The parent delivery row could also show the number of deliveries, and how many were delivered so far, next to or above/the ETA (ex: "2/5").
The indented list should display each partial delivery, have its ETA and allow it to be marked as "delivered", resulting in a partially completed delivery.
I apologise if this post sounds demanding, I just work in tech as well and was trying to be thorough for the "ticket", and save some time in UX research :)