The answer would be the same if the parents are both citizens.
“If they were an infant, and their parents wanted to leave the United States with them, could the United States government prevent their parents from taking them?” How would the US stop them from taking their baby overseas if the parents are citizens?
“If the infant’s parents were deported, would the United States government prevent them from taking their child with them under a claim of the infant being a U.S. citizen? “ Again, what law would stop them if they were US citizens?
“If they were an infant and their parents died, would the United States government prevent their grandparents from returning them to their mother country?” Would the US government stop natural born citizens John and Jane from having their British mom come take the baby if they died?
Very interesting questions.
It would seem axiomatic that the U.S. Government can’t deport a natural born citizen of the U.S.
OTOH, the U.S. government is not categorically prevented from doing a two step against a treasonous naturalized U.S. citizen: First stripping them of their U.S. citizenship (e.g., under a theory of fraud) and then unceremoniously shipping them back to the country of which they were originally a citizen.