HEy R.
First let me just say that some mamas need to have compassion for their fellow mamas. Motherhood and all it's responsibilities is tough enough without having other mamas knock you for doing what YOU think is best for your situation.
Firstly, I say print up tshirts for your trip that say IT'S NOT POLITE TO STARE! or STARING IS RUDE! or PLEASE BE PATIENT.
Now for a 4 hour layover I would have what you already said you have ready to go : DVD player and activities. Your little fella will need to get his wiggles out so I say be prepared to let him roam tethered to you. Just stay close and redirect when necessary. Check with the airport to see if they have a play area or an area where he can run about. If not, find a corner somewhere and make it your own little play area...with toys that he didn't see on the flight. I would take small play doh containers, dot painters, assorted stickers, packing poppers, colored pipe cleaners, straws and large fruit loops, clingy thingys for windows, viewfinder, feathers, and so on.
Make sure it isn't expensive or valuable so if it gets left behind/lost/tossed it won't matter. You might want to dump some of that stuff anyway to lighten your load after the 4 hour layover.
Lastly, never apologize for your way of parenting. No one loves your little fella more than you...and you are doing your best.
Let me add, my cousin's grandson got away from his other grandmother and ran out between two cars. He was hit. Broken leg. Broken arm. Skull opened exposing his brain. He is on the road to recovery but it was horrible.
Didn't mean to freak you out. Just thought I would share the benefits of using a harness/tether/leash. Be safe and have a wonderful trip!