"Children are subject the citizenship laws of their parents, DV. If you are a citizen of a country A and give birth to a child in country B, the child is a citizen of country A. That's what Mexico's law says about Mexican citizens, and what US law says about children born to US citizens abroad.I'm pretty sure that children (and their parents, as well) are subject to the citizenship laws of the country they're in, and that the citizenship laws of one country are not automatically binding on the citizenship laws of another (though of course, country "A" can legislate that the citizenship laws of country "B" have a little/some/full weight, according to the laws of country "A"--in effect adopting portions of the foreign law into their own law, if that's what country "A" decides to do.) In cases where a child is born to one or more US citizens outside of the US, it is the US that gets to decide whether that child is/is not a US citizen, and to do so regardless of what the citizenship laws are in the country of that child's birth, or the home country of his non-US parent. That is according to US law. The country in which the child is born, as well as the home country of the non-US parent also has jurisdiction, however, and can grant or withhold citizenship in those countries, according to their own laws. Where the citizenship laws of the foreign country conflict with the citizenship laws of the US, there is generally more law to deal with the conflict, often by allowing the child dual citizenship as a minor, and giving him the responsibility of deciding his/her final citizenship at the age of maturity. (Where all else fails, physical presence in the US rather than the foreign country counts for a whole lot.)
Any other interpretation is a clear mis-reading of the intent of the 14th."
Mexico (and all other countries) can do what they wish (including offering /withholding citizenship to whomever they believe to be under their jurisdiction (either by birthright, or by physical presence), and even by offering citizenship to a child that we in the US also offer citizenship to, if that's what they wish). Here in the US--for US citizens and their progeny here and abroad, as well as for children born here on US soil--because that's what US law says----US citizenship law is the only law that matters.