I don't think that would be the case.
I am a US citizen and my parents aren't (I was born over there while mum and dad were living there, dad was in the Aus Navy)
We went back to the US when I was 12 and when we got to USA we had to go through the American line and both of my parents got to come through the American line with me as I was a minor, mum and dad loved it as the American customs line was a lot smaller than the foreigner line
It sounds like your DH and DS will be in a similar situation and I think this will be the case for them, I highly doubt they'll seperate them with your DS being a minor.
Hope this helps!