I know you're just trying to pull something out of thin air that sounds plausible, but...this would be simple to prove with a request for valid death certificates, marriage license, and a birth certificate to prove you were married, the child is yours, and that both are in fact deceased. Oh, and of course, you'll have to prove who you are as well.
It may be simple enough to prove, but that is an uncomfortable ask if those circumstances are genuine.
Given the (rightful) outcry about handing out your IDs to private corporations in "safety"'s name, are you really suggesting providing documents even more specific about you?
We're all worried about identity fraud, and such documents are actually used to apply for an id in some countries!