Let us say I've got a datastore that consists of mother, father, and child objects. Inside the oldsters objects I've got a area known as child which stores a mention of the the youngster. Can you really reference this child from both mom and dad without creating duplicate child instances for every (in design for OOP). Is how databases work on all?

Yes, you should use the db.ReferenceProperty to complete just that.

A reference property simply stores the initial key from the entity it references. So the oldsters organizations could each have a copy from the key akin to the youngster such as this:

class Child(db.Model):
    ... # child properties
class Father(db.Model):
    child = db.ReferenceProperty(Child)
    ...
class Mother(db.Model):
    child = db.ReferenceProperty(Child)
    ...