All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the state wherein they reside.
The Supreme Court has not (yet) explicitly ruled on whether a visitor or illegal alien is "subject to the jurisdiction of the United States".
If Congress did not intend that phrase to have meaning, they would not have included it.
1. The innocent unborn child is, at birth, immediately subject to the jurisdiction of the United States.
2. The illegal alien parents can be arrested, jailed, fined, and imprisoned by a US Court. They are subject to the jurisdiction of the United States