多谢8老师 ！Great to know "the mom leaving does not affect the kid's green card validity"!
A follow-up question: What if the mom abandons her green card (i.e. does not go back to the US)? Will that affect her son's green card validity?
-No. It is irrelevant to the kid if the mother voluntarily abandons her green card.
Does it make a difference if the son is younger than 18 years old (or older than 18 years old) when the mom abandons her green card?
-No difference.
