Obviously if someone has to be blamed then it should be the parents. Did they forget to carry their green card with them? No, because they would not have been able to enter US back and would have got the same treatment from US officials. Perhaps maybe even handcuffed and deported back. So what are they nagging about Indian officials? If they say they have been in US for 9 years then they should have known better. Rules are rules! Get your papers right next time.
