I think something every country will legally agree on is that laws apply only to citizens. Laws are a binding contract that in return for following the rules, you get protection under the rules. People who are not citizens have not signed the contract, thus are not protected. Morality is a different question, but what's intresting is that in 2015, the circuit court actually stated that it was unethical to keep families together, which is why they must be separated if the parents do not consent to leaving the country with their children when they are forced to leave (after Obama attempted to create an executive order that all families must be deported together).