You are correct in that according to Article 2 Section 1 of the Constitution a person must be a Natural Born U.S. Citizen (NBC) to be eligible for POTUS. A NBC is a person that is born on American soil to parents that are U.S. citizens.
In mathematical terms:
1 (both parents are US citizens) + 1 (born on American soil) = 2 (qualified per the constitution to be POTUS).
For OBAMA we have:
0 (both parents are US citizens) + 1 (born on American soil) = 1 (not qualified for POTUS)....
0 (both parents are US citizens) + 0 (not born on American soil) = 0 (not qualified for POTUS.
Therefore, it does not matter where OBAMA was born. He is not eligible for POTUS because his father OBAMA Sr. was born in Kenya and was a British citizen.
Wrong. This tells you who is a citizen at birth (natural born citizen): http://www.law.cornell.edu/uscode/8/1401.html. There is no definition of "natural born" in the Constitution, so you are in error when you assume the parents had to be citizens. In fact, under English common law, which was what was in use in the colonies, the place of birth ALONE determined citizenship. We didn't adopt a new system. We simply continued doing what we had done before independence, under England.