Well, if Mary's recollection is accurate, either the man we now call "Barack Obama" is using a false birth date or that baby Mary babysat for was not him.
I’ll leave it with you to think about.
Clever girl that 'Ann Obama' - she's listed in the Polk in Honolulu as well as Anna Obama in the Polk Seattle - BOTH FOR 1961 - 1962
http://myveryownpointofview.wordpress.com/2011/02/05/pssst-hey-buddy-wanna-see-my-polk/
all the Hawaii address listings are at the above blog.
Barack Obama Senior claimed paternity of Honolulu born Barack Hussein Obama, II on August 31, 1961 in an interview with an Immigration and Naturalization Service Agent.
http://www.wnd.com/files/2012/07/INS-6.jpg