Is there a technique (or add-on) to automatically select a parent item's children too?

Some operations only apply to the child elements if you navigate through the entire parent-child-subchild-etc. hierarchies to manually select every nested item and this can be a huge pain if you try to organize objects and other elements logically by nesting them. Delete is an obvious example, and I think hiding is as well. I think there was some other operation I ran into this issue with too, but I can’t recall off hand what it was. I know going to the outliner and selecting “Delete Hierarchy” works, but it would be preferable if that were the default behavior, or at least works with a keystroke.

I modeled a medieval house that was somewhat complex and it became a huge headache. Is there a way to make it less of one?

There’s Select > Select Grouped > Children (check Extend)
Hotkey: Shift + G

I will try this later, but assuming it works, THANK YOU.

To add to above answer… [ and ] in object-mode in the 3d-viewport navigate the object hierarchy … hold down shift to extend selection as you navigate.
Can also right-click on an option in the outliner’s right-click menu to assign a shortcut. Made my Select Hierarchy in the outliner Shift-G so it’s similar to 3d-viewport.
Good luck.