Hispanos in blue, Blacks in purple, Whites in yellow. Click to enlarge. From National Review Online.
The American birth rate is the highest it has been since the end of the baby boom (1961). Besides more people having children, another reason is the decrease in abortions. The major reason though is the higher birthing rate of minorities in the United States. Blacks have a fertility rate slightly above 2.1 while Hispanos fertility rate is almost 3.0. The fertility rate of Whites is actually below that of France. A final reason for the increase of population (from 1961 to 2007 the fertility rate was in negative growth direction) is immigration. The good economic and political freedoms of the United States have attracted people from all over the world.
To avoid negative population growth and to stay out of the "needs babies" category America must remain free, value life, and be open to a form of immigration. Lacking one of these three traits would make the United States like the other first world countries in a demographic spiral.