REPOSTED FROM #483 
It really all boils down to which child was born in Hawaii, and which child Mary babysat in January 1961. The family group shows the kenyan with Ruth, and she's holding the half-black child which is Mark, who was born after she went to Kenya in late 1964. So Mark, although he hasn't actually said so, was born in 1965.
That leads to the question, who is the dark boy who is tall enough to reach her waist, in approx 1966?
If he is, as he appears to be, the same dark child sitting next little zero, then those two little boys were both born in the same year, the dark child being just a little older, and somewhere, somehow they were in the same place at the same time...one could assume in Boston, which is where Stanley Ann Dunham told Susan Blake she was going that very same day of her visit... And that's why the kenyan was able to tell friends at Harvard he was visiting his son. Which is what led the Harvard faculty to believe he had 'another wife' in Boston.
The dark child went to Kenya and lived with his father and stepmother. And the lighter boy shows up aged about two, with Stanley Ann Dunham in Hawaii, in 1963 in a photograph, when legend has it, she took him to the zoo.
Obama Sr. married schoolteacher, Ruth Baker, five months after his divorce to Ann Dunham, the mother of President Obama. The relationship produced two sons, Mark Okoth Obama (1965) and David Opiya Obama (1967-1987). The couple filed for divorce in 1973, and Ruth remarried a year later to Tanzanian businessman, Ndesandjo, and the two boys took his name. Mark, who holds a BSc (Physics) from Brown, an MSc (Physics) from Stanford and an MBA from Emory, runs a China-based internet consulting firm. His brother, David, died tragically in a motorcycle accident in 1987.
http://2012.presidential-candidates.org/Obama/Siblings.php
So for anyone still following this, Mark was born in 1965, the family group photograph shows Ruth holding Mark as a toddler, the dark boy who was photographed sitting next to zero, was born in 1961, so that same dark boy was FIVE years old in that family group image.
There’s no room for a ‘David’ in any of this story. ‘David’ is just the name they gave to the dark child whom Mary babysat in January 1961. And when you figure it out, you’ll have had the same epiphany we did. The light will eventaully go on.
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Obama has half-siblings from his father’s first and third marriages in Africa .
Malik Obama (half-brother ) (b 1958)
Auma Obama (half-sister b 1960)
Abo Obama (maybe adopted half-brother b 1968)
Bernard Obama (maybe adopted half-brother b 1970)
Mark Ndesandjo ) half-brother by father’s third wife b c.1965
David Ndesandjo (1967-1987) half-brother by father’s third wife,
George Hussein Onyango Obama ( illegitimate half-brother, b c 1982)
http://wiki.answers.com/Q/Who_are_Barack_Obama’s_siblings