Children are awkward for libertarians. We mostly think we have a right to be left alone, not to assistance from others. But infants clearly have a right to more than this, implying a positive duty on someone else, "the parents!" a libertarian might cry. But it doesn't take much imagination to see that this isn't enough to protect the rights of children, some are still going to be abandoned and abused and they shouldn't need to rely on charity to get some help. So the government should guarantee these rights.
Of course, even if we take a minimalist, negative view of rights, we all have them, we talk about human rights all the time; not citizens rights, or South African rights. People in certain countries have these rights violated all the time. The cry is usually that it is their governments duty to enforce these rights. Maybe we should put pressure on delinquent governments but we have no duty ourselves. I think this is wrong, if we talk about human rights then we should face up to our (negative) duty.
I'm sceptical of arguments by analogy like this one, but I think it's something worth thinking about.
Governments create new rights for their citizens all the time. I don't see any problem with these rights only applying only to their citizens, but we should remember what the most basic fundamental rights are and what they should imply.