The key is that the child’s parents were LEGALLY in the U.S. unlike so many illegals and their babies.
Wong Kim Ark and later cases shows that illegal aliens are subject to the laws of the United States.
Jurisdiction Clause
https://legalclarity.org/what-does-subject-to-the-jurisdiction-thereof-mean/
Under the rule established by Wong Kim Ark and reinforced by later cases, birthright citizenship applies to children born in the United States to lawful permanent residents, temporary visitors, and undocumented immigrants alike. The parents’ immigration status does not determine whether their child is “subject to the jurisdiction” of the United States.
The Supreme Court addressed the status of undocumented immigrants directly in Plyler v. Doe (1982). That case involved a Texas law denying public education to children who were in the country without authorization. The Court struck down the law and held that the 14th Amendment’s protections extend to every person within a state’s territorial boundaries, regardless of how they entered the country.6 The Court reasoned that a person’s unlawful entry does not place them outside the jurisdiction of the state where they physically reside. If you are present in the United States and subject to its laws — meaning you can be arrested, taxed, and prosecuted — you are within its jurisdiction.
From Wong Kim Ark.
I think the key part in the ruling that explains this is below.
His allegiance to the United States is direct and immediate, and, although but local and temporary, continuing only so long as he remains within our territory, is yet, in the words of Lord Coke in Calvin’s Case, 7 Rep. 6a, “strong enough to make a natural subject, for if he hath issue here, that issue is a natural-born subject;”
Wong Kim Ark (1898)
Plyer vs Doe (1982)
https://supreme.justia.com/cases/federal/us/457/202/