Filter by parent – child

Hi,

I’m trying to make multiple filters (dropdowns) with categories. That’s because we can either use Categories or Tags… So I want filter A to be Parent category – child, filter B, Parent category – child, etc.

The issue I’m running into is that I want to be able to filter on parent-child relation.

If necessary I can provide an URL, but would appreciate not put it out in the open 🙂