Okay, this is out there, but all we HAVE is speculation now, anyway.
So, the Vaults were known for being far more than just ways to survive nuclear war. They were, in fact, almost always designed as ~experiments~ of some kind or another. Since Vault III is near MIT and post-Fallout a tech center, it would not be unreasonable to think that that Vault might have been designed with a technologically complicated experiment in mind. Cryogenics, for one. But cryogenics, in itself, is not really THAT much of an experiment. I mean, it works or it doesn't, but most of the vaults had an aspect of ~social~ engineering to them.
So what about this ---- Vault III is designed to put people into cryostasis, yes, but ala Tranquility Lane they are also subjected to experiments designed to keep their minds active. Whole theory is blown out of the water if the mind is dormant while frozen, but who knows? And of course, re-hashing Tranquility Lane may be too cliche.
But say you have these 1950's-style scenes play out, then you get frozen, then you wake up and find that you are the Sole Survivor of Vault III... at first, you may think those memories of spouse and child are YOURs, but through some means you determine / guess that they are NOT your own memories, but were implanted. It was a sort of "pre-War preparedness drill" mental construct. Perhaps you were even frozen BEFORE the bombs actually DID fall, and were being tested to determine how people would react when the event actually did happen? Then it really DID happen, while you were under stasis.
What prompted this hair-brained theory was that scene with Codsworth; the PC is clearly not long out of the Vault and while he does muse that "maybe there are other survivors"... he doesn't say, "Maybe Nora and Shaun survived!".... it just seems like they would be his first concern, not just "any" survivors, but -them-. But if he knew they were constructs of a program that ran in his mind while he slept... then he would not care about them because they were never real.... so his concern for "any" other survivors would be more appropriate.
This would have the added advantage of freeing up the 'back story' of the character, so that those who don't like the idea of being forced into being a character who has a loving spouse and child can build up a back story that's much more flexible --- all you have to determine is why your character was selected to be placed into Vault III (which may have been a test facility before the bombs even fell). Could be any number of reasons for -that- without forcing a story onto the character.
Of course, as noted all over the place (particularly in threads where the spouse/child are believed dead), this would mean you went through the trouble of creating your spouse for "nothing" if they never show up again.
EDIT: Not sure how this may influence things but in another thread I was reminded of the "Memory Den" we see in some shots. So dabbling in memory transfer may not be that far-fetched. Although it may, also, have nothing to do with the character creation.