A pregnant woman crosses the border illegally from Mexico into the U.S. and gives birth to her child in a U.S. hospital. The child is an American citizen, fair enough, no argument here. My question is if the child also possesses Mexican citizenship? Some obvious option that cross my mind.
The child possess dual citizenship until at some point (age 18?) he the child formally expected to make a declaration about which single country in which to claim citizenship?
The child possess dual citizenship forever.
No Mexican citizenship regardless of the status or choice of the mother. The child wasn’t born in Mexico and the government there doesn’t have any interest in the child.
The only practical effect of that is that a dual citizen will only have the U.S. citizenship recognised by the U.S. Government. So, for example, you must enter the U.S. using a U.S. passport if you are a citizen, you cannot get a U.S. visa, and you cannot seek consular assistance from Mexico if arrested for a crime in the U.S.
Some countries do require their citizens not to be dual citizens, and require them to make a choice – China is an example – but neither Mexico nor the U.S. do.
That column mainly discusses how you can acquire dual citizenship by naturalisation. It gives the specific case of a U.K. citizen being naturalised as a U.S. citizen:
Before 2002, an Australian citizen becoming a U.S. citizen by naturalisation did lose their Australian citizenship, but that was by the operation of Australian law – not U.S. law – and Australian law changed, so now they don’t lose Australian citizenship.
However, the case in the OP is of a child being born to Mexican parents in the U.S. while the mother is unlawfully present in the U.S. That child does not ever have to choose, and will remain a dual citizen, unless:
(1) he or she voluntarily renounces either citizenship, or
(2) he or she is naturalised as a citizen of a third country which requires its naturalised citizens to renounce other citizenship.
As noted by Giles above, there is no requirement for a child born with dual citizenship to renounce his or her U.S. citizenship later in life. From the State Department (bolding mine):
Also, the Staff Report you linked to above only deals with people who acquire a second citizenship via naturalization. In general, you can only lose U.S. citizenship by performing certain actions; having a second citizenship from birth is not among them.
“Anchor baby” is a complete misnomer. The premise is that by having a child in the US, the mother secures some kind of status for herself. But this is totally unfounded. The child can’t help the mother get legal status in the US until the child is 21 years old.
Becoming naturalized in another country does not result in loss of US cicizenship unless the other country requires renunciation of previous citizenship as a condition of naturalization. I know this from personal experience. Essentially, the only thing you can do to lose US citizenship nowadays (it wasn’t always so) is renounce it.