My wife was a foreign National from Thailand and we married/she received a K1 marriage Visa. After renewing her green card numerous times, she successfully became a Naturalized US citizen in 2016. Subsequently we received IR-2 green cards for her two boys who were 9 & 11 years old in 2017. The boys have US social security card numbers and a US Passport. We live in Thailand but travel to USA annually. Do they disregard the green cards as they will use their US Passports for Intl travel? The IR-2 category was granted to them as they were under 18 years old. Does anything change once they turn 18 years old re: their category status (IR-2 category status)?