If he has been physically present in US for periods totalling five years or more, then his children are eligible for US citizenship by descent. He can apply for their US passoports before bringing them to US
If ha has not been in US for at least 5 years (collectively, add up the days spent in US on every trip) then he cannot get citizenship for his children based on his US citizenship. He will bring all his unmarried children under 21 to US with IR visa, and for each one that is under 18 when admitted to US apply for their US passport after admittance as Permanent Residents.
The derivative benefit that awarded the father citizenship is most likely "citizenship through descent", with his father meeting the requirements for passing citizenship to his children born outside US.
Under current law, the US citizen parent needs to spend a total of five years in US territory, with at least 2 of those years being after the citizen's 14th birthday. There are special rules that allow time spent abroad to be counted towards this requirement. Citizenship through parents
One parent is a U.S. citizen at the time of birth and the birthdate is on or after November 14, 1986
The U.S. citizen parent had been physically present in the U.S. or its territories for a period of at least five years at some time in his or her life prior to the birth, of which at least two years were after his or her 14th birthday.
If the U.S. citizen parent spent time abroad in any of the following three capacities, this can also be counted towards the physical presence requirement:
Additionally, time spent abroad by the U.S. citizen parent while the U.S. citizen parent was the unmarried son or daughter and a member of the household of a person who meets any of the three conditions listed above can also be counted.
- Serving honorably in the U.S. armed forces;
- Employed with the U.S. government; or
- Employed with certain international organizations.
The child was under 18 or not yet born on February 27, 2001
At least one parent is a U.S. citizen, the child is currently under 18 and residing in the U.S. in the legal and physical custody of the U.S. citizen parent pursuant to lawful admission for permanent residence.