In essence, she was not old enough to qualify her son for automatic U.S. Citizenship. At most, there were only 2 years elapsed since his mother turned 16 at the time of Barack Obamas birth when she was 18 in Hawaii. His mother would have needed to have been 16+5= 21 years old, at the time of Barack Obamas birth for him to have been a natural-born citizen. Only if he was born outside the U.S. If he was born in Hawaii, he is a natural-born citizen under the 14th Amendment, even if neither parent were a citizen.
The 14th Amendment does not dictate that result. The 5th clause of it says that "Congress shall enforce this item with appropriate legislation." Congress has passed laws, for instance, which provide that children born of foreign diplomats are citizens of their own nations, not of the US, even if born in Georgetown University Hospital.
The anchor baby problem is soluable, IF Congress would get off its duff and write the necessary legal definition of citizenship at birth.
John / Billybob