Give that the child was born in Mexico before his father became a U.S. citizen, and his mother is not a U.S. citizen, the father's best option is likely to petition for the child to enter the U.S. as a permanent resident. Subsequent to his entry as a legal permanent resident, as long as he remains in his father's legal and physical custody (even if shared with the mother), he will become eligible for U.S. citizenship under the Child Citizenship Act of 2000.

