It's Texas! (The only other acceptable guess was Arizona.) The idea of repealing the 14th Amendment in order to prevent children of undocumented immigrants from becoming citizens is in the news at the moment because Donald Trump and Scott Walker have proposed it, but it turns out that the Lone Star State is already accused of giving the Bill of Rights a runaround on the issue:
A group of mothers has filed suit against the chief of the state's Department of State Health Services Vital Statistics Unit, because it has refused to give their U.S.-born children birth certificates ... The issue in this case is what kinds of identification Texas can demand of their undocumented immigrant parents to issue a birth certificate.
According to the complaint, Texas is refusing most forms of ID that undocumented immigrants would have access to.
That's from an excellent July 23 NPR story, which you can read here. Texas says that its decision whether or not to issue a birth certificate is a matter of state control that's not subject to federal jurisdiction (the suit is filed in federal court) and that it's justified in rejecting the documents in question.
To be clear, Texas' actions do not constitute a formal claim that the children of undocumented immigrants are not United States citizens. Plaintiffs say, though, that not being issued a birth certificate constitutes unlawful discrimination because it creates an obstacle to obtaining day care, medical care, "and other health, education and welfare services requiring parental consent."