My understanding is that it will need to be converted to a Windows 7 compatible folder somehow.
But also, I was under the impression that it didn't matter. For instance, I play Sims 3 on a laptop that runs a newer version of Windows than the Desktop computer I use to view the forum. When I created a file and moved it to the desktop computer to be printed, all that happened was that the file had to be viewed in compatibility mode - there was no issue with anything not being recognised.
My understanding is also that folder types do not matter - I thought that a Windows Folder was a Windows Folder.
I don't quite get how a folder wouldn't be reecognized by the launcher, unless the folder is in the wrong place or not there at all.
EDIT: The saves system was changed from files to folders with an EP. Does your son have the same EP's as you? If not, that could be the cause.
EDIT 2: Elaborating on that, did your son use any Content (E.G Store/EP/SP/CC) that he doesn't have, but you do, to create his save? Are you both on the same patch level?