Babies born in USA (50 states) are citizens.
18USC ch12 (III)(1) 1401
If you are born in the USA there is no stipulation that your parents have to US citizens. It just is by law.
Aboriginal Americans (Indians) who were subject to tribal jurisdiction were not even US citizens until 1924, by a congressional act.
Being born a citizen does not necessarily make one eligible for the office of POTUS under Article II, section one, clause 5. A person made a citizen at birth via the Immigration and Naturalization Act does not even have to be born in the US, ala Ted Cruz.