Hi, I'm Ashley. I am a writer on educational topics for UK Students.
Add in the fact that he didn't just appear as the same age he was when he went back. He was a baby and they would have watched him change and grow gradually, thus negating the impact of 'recognising him'.
Never heard of "A Separation" or "Asghar Farhadi". Got to go check this out now. Will let you know if I agree!