The Potters did not know that Voldemort was after their son specifically, only that they were in general danger from the Death Eaters by being opposed to them and also active members in the Order of the Phoenix. At this time, they were hidden by the fidelius charm, which is some pretty serious magics: "As long as the Secret Keeper refused to speak, You-Know-Who could search the village where Lily and James were staying for years and never find them, not even if he had his nose pressed against their sitting room window!"
Voldemort only went for their son after Snape told him of Trelawney's prophecy, which was immediately after it was spoken, making very little time for McGonagall to inform Dumbledore and for the OotP to react. (Even supposing they could decipher the prophecy instantly.)
Also, the note from Dumbledore specifically says that James left the cloak in Dumbledore's possession before he died. (Maybe to prevent it from getting into Voldemort's hands.) This explains why the cloak was not available when then Potters needed it the most.
Really late reply, but: the prophecy was made before Harry was born; Voldemort and Dumbledore found out about it at roughly the same time (almost immediately); and the attack came when Harry was fifteen months old. They knew about the prophecy while they were in hiding.
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 96. The previous thread is at almost 300 comments.
There is now a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system.
Also: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, .
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: