That's only true if the child is born abroad. If the child is born in the USA, unless the parents are diplomats, invaders, or travelers in transit, the child is a natural born citizen, irresepective of the parents' citizenship.
The child must meet the following requirements:
Have at least one American citizen parent by birth or naturalization;
Be under 18 years of age;
Live in the legal and physical custody of the American citizen parent; and
Be admitted as an immigrant for lawful permanent residence.
In addition, if the child is adopted, the adoption must be full and final.
At least one parent of the child is an American citizen by birth or naturalization.
The American citizen parent has been physically present in the United States for a total of at least five years, at least two of which are after the age of 14. If the child’s American citizen parent cannot meet the physical presence requirement, it is enough if one of the child’s American citizen grandparents can meet it.
The child is under the age of eighteen.
The child lives abroad in the legal and physical custody of the American citizen parent and has been lawfully admitted into the United States as a nonimmigrant.
http://travel.state.gov/visa/immigrants/types/types_1312.html