Not to be a pessimist but...

I think that the whole "It could have been a still birth wrapped up and buried respectfully with the tree" theory just doesn't have any logic to it. Why would you bury that in a RUG? Also, hospitals existed in the 60s, and there's only been one family who lived there so the daughter most likely would have known and mentioned that. And if you miscarry... that usually doesn't really get buried unless you're really far along. But by then, they probably would have ended up at the hospital and not just bled out in their house.

Sometimes the most obvious solution is the correct one.