John. Figure two hours from the GW Bridge as you calculate driving time. Local hotels are plentiful within minutes of the Allentown Fairgrounds and are near a very interesting DaVinci Science Center. You and your son might enjoy that. Also, I believe there are some YouTube videos posted on recent Allentown train shows which will give you a feel for the event.
Two hours from the GW and another two hours to get across the stinkin' bridge!