When the children’s green card is scheduled, the parents become citizens, how to calculate the schedule?

Keep the original schedule. If the parents of permanent residents apply for their children with 2B priority, then when the parents become citizens, they will immediately become the first priority. The children will still maintain the original waiting list and can obtain a green card faster. The priority date for relative immigration starts when the applicant's relatives are immigrated and the application form I-130 is submitted to the Immigration Bureau.