Yep, this is what we do as well. I have a link on the tag details page that goes to a Parents of Tag members page. This page lists parents plus the relationship types specified in the query for all the people in the that tag (or in any tag below!). It's like a very advanced "List" that you can run on any tag with one click. This has been an immensely useful tool for us.
The queries and installation instructions are in my google drive folder: https://goo.gl/gUwx7P / Erik's Stuff / Child Tag Pages. If you have trouble accessing, just let me know.
I have seen some put parent emails on the kids records, so you would send an email to a class of kids and it would go to the parents. I have been advising against this as it's harder to maintain those emails when they change, and the tool above makes this unnecessary.
I went to a Rock demo workshop a few months ago at CITN and found it interesting how differently they handle this. A kid can totally be a member of multiple households. I'm not sure if I like this better. Seems confusing. In my experience there has been a primary parent that we happen to see more and communicate with and another that may or may just want to just be in the loop, so we use the relationship type for them.