My thoughts are along the same lines as JAP's last post. That memo, together with the mother's death certificate, certainly implies that Thomas didn't die in childhood, as might have been the case if his mother had died of some infectious disease, say. Incidentally, their father died in 1904, some four years before the memo.
I'm in danger of becoming obsessive about this, but reading the memo in her own handwriting is beginning to give me goosebumps . . . these personal stories are what makes genealogy so fascinating.
Mike.