Yeah, I was reading somewhere that Hawaii twins were born the same day Obama was, but their birth announcement was missing from those Hawaii newspaper ads. This suggests that their’s was deleted and Obama’s inserted in their place.
The Nordyke twins (not identical - look at the dimples) are supposed to be the two girls in the middle of Obama's row in that class picture. Here's a larger view courtesy of obamafile.com
The fact they were in the same class reinforces the "same birth day, so where is the announcement" question. That can be explained in other ways, however.
The important point is that records that would clarify specific birth data for Obama are "missing".