University diplomas and credit cards are not identity documents anyway as they don't tend to have your picture on them. Well, I guess in some countries, credit cards do. My advise, send a copy of the letter back along with your own letter where you go through their whole list of id documents and state, "the child does not have an age of majority ID card because it has not reached the age of majority, the child does not have a drivers license because it is not old enough to drive, the child does not have a university diploma because it is not old enough to have started school yet, let alone university etc. What you can offer in return is another copy of the childs passport (or the mothers) and you could offer a letter from the childs pediatrician stating, I have seen the child of (mothers name) and (your name), the child is born on (date) and is a patient of mine. Maybe they will accept that as a better than nothing. Could it be that they want the child to have its own passport? Could this be arranged?