If you need a taxonomy field to be filtered based off of another taxonomy field's value, this module is for you. It is handled via Views.

I originally used Business Rules to accomplish the filtering but Business Rules only allowed filtering of one child when we needed multiple. That is all this module does where Business Rules has a lot of other things; not just dependent fields.

This module handles multiple dependencies so if you have a field that needs to filter multiple fields in your form, this module can handle that.