This case has always been a heartbreaker and a real mystery.
I really believe that someone out there knows or knew something about this little boy, but for whatever reason, possibly ignorance, is not telling what they know.
My former husband was born in Philly in 1955. Both sides of his family had lived there for several generations. Strictly reared as Catholics, his Mother's Mother had 10 children. Only it turned out, as my ex and I found out many years later, that wasn't the whole truth. One of his "Uncles" was really his cousin.
My MIL's twin sister became pregnant at 15. This of course would not do in 1945. In a very strict and very Catholic household. So the plan was that the family moved to a different neighborhood where nobody knew them, send the girl off to a home for unwed mothers (possibly the school for wayward girls) and when the child was born, he would be raised by his Grandparents as "their" child, and woe be to anyone who ever said a word about the arrangement to anyone else.
Noone ever said a word.
The only way it came out was that when the said child went to enlist in the Army years later, they were the ones who told him that the Mother he named on his enlistment papers didn't match his actual Mother's name on his BC, (there was no formal adoption) and the enlistment officer was suspicious.
And the said young man STILL never confronted his family. The only reason it came out was that he and a close in age nephew/cousin got drunk and started talking about their Vietnam War experiences. Then the bombshell about the Mother/Sister.
My ex's brother, the one he confided it to, told my ex. He could not contain his amazement at this, and asked his Mom about it. She explained how it all came about and then left us with the plea that "we never talk about this again, ever, don't bring it up anywhere at any time". And this was in 1976, but the shame was still there. As far as I know, noone ever talked about it again.
I could easily see a scenario where the boy in the box was someone's brother or cousin, and was told by family that he died, and that was that, and don't talk about it any more, ever!
Especially back in that time, in any number of circumstances.