Do not take a coach ticket on Southbound Washington-bound Amtrak trains out of EWR rail station on Sat and Sun afternoons. Even if you've a ticket on a "reserved" train, the ticket is just for the right to get on the train. A seat is not guaranteed. Never found one. Stood all the way to Trenton. The fact that it was only a 35 min ride made it somewhat tolerable. Going to Philly (an hour) or further south will be harder. I found kids sitting on the luggage in the aisles of this so-called reserved train.

If you've to take a train, look for The Keystone train that goes to Philly and west to Harrisburg. It might be less full without the Baltimore and Washington passengers.