Django: use content_type of parent model for GenericTabularInline

Question

In Django 1.8, I have a parent class and a child class, which are not abstract:

class Parent(models.Model):
    ...

class Child(Parent):
    ...

and I have another model, which has a GenericForeignKey:

class Tags(models.Model):
    ...
    content_type = ...
    object_id = ...
    content_object = GenericForeignKey(...)
    ...

Now I want to build ParentModelAdmin and ChildModelAdmin such that both show the same list of tags as an inline (TagsGenericTabularInline).

How can I achieve that?