The children born in the United States to illegal alien mothers are often referred to as "anchor babies."
Under current practice, these children are U.S. citizens at birth, simply because they were born on U.S. soil. They are called anchor babies because, as U.S. citizens, they become eligible to sponsor for legal immigration most of their relatives, including their illegal alien mothers, when they turn 21 years of age, thus becoming the U.S. "anchor" for an extended immigrant family.
While there is no formal policy that forbids DHS from deporting the illegal alien parents of children born in the U.S., they rarely are actually deported. In some cases, immigration judges make exceptions for the parents on the basis of their U.S.-born children and grant the parents legal status. In many cases, though, immigration officials choose not to initiate removal proceedings against illegal aliens with U.S.-born children, so they simply remain here illegally.
Thus, the U.S.-born children of illegal aliens not only represent additional U.S. population growth, but act as 'anchors' to eventually pull a large number of extended family members into the country legally. In fact, an entire industry has built up around the U.S. system of birthright citizenship. Thousands of pregnant women who are about to deliver come to the United States each year from countries as far away as South Korea and as near as Mexico so that they can give birth on U.S. soil. Some come legally as temporary visitors; others enter illegally. Once the child is born, they get a U.S. birth certificate and passport for the child, and their future link to this country is established and irreversible.