Call Aeroflot's DC office and push to speak with the manager. Perhaps he can arrange an escort/flight attendent to bring the kid through customs/passport control. This is a more complex problem than getting a gate pass

Contact for Aeroflot, buried on their website (not sure if I can post a phone number):

http://www.aeroflot.ru/cms/en/office_items/261

If you can't get in touch with the DC office (and I assume they close precisely at 5pm), go to the Aeroflot checkin counter before the plane's arrival and beg to speak to the station chief (the front line people are probably contracted).