models.py

from django.db import models
from django.shortcuts import _get_queryset

class ChildAwareModel(models.Model):
    class Meta:
        abstract = True

    def get_child_model(self):
        """
        Attempts to determine if an inherited model record exists.
        New child relationships can be added though the inner class Inheritance.

        class Model(ChildAwareModel):
            ...

            class Inheritance:
                children = ( 'yourapp.models.ChildModel', )
        """

        def get_child_module(module, list):
            if len(list) > 1:
                return get_child_module(getattr(module, list[0:1][0]), list[1:])
            else:
                return getattr(module, list[0])

        if hasattr(self, 'Inheritance'):
            children = getattr(self.Inheritance, 'children', [])
            for c in children:
                components = c.split('.')
                m = __import__(components[0])
                klass = get_child_module(m, components[1:])
                qs = _get_queryset(klass)
                try:
                    child = qs.get( **{ 'pk':self.pk } )
                    return child
                except qs.model.DoesNotExist:
                    pass
        return None