I believe it doesn t matter, the only reason why there are two different lines is to speed up the process, because US citizens/US Permanent Legal Residents pretty much just go through...Also, just because you hold a UK passport doesn t mean you have to separate because you could be a Legal Resident (green card) but anyway, whatever your legal situation may be, I believe you can go as a family together through the US Citizen/US legal residents line. CBP officers and their stations are equipped with the stamps and the fingerprint machines to handle both situations. I would suggest once you get off the airplane you ask a C.B.P. officer before you got through Immigration, so that you don t waste time in the wrong lineYou can always call USCIS National Customer Service Center (NCSC): 1-800-375-5283.
You could wait with your husband and son, it s all computerized.
It doesn t matter, you will be waited on any line .