A.H.
Ok so I have traveled by plane many many times with my kids and here are my tips. Sorry this is quite long-winded but I really think through my airline travel!
1) I would never EVER travel through the airport with my 2 year-old without a stroller. I just use a basic light umbrella stroller but if my little girl isn't strapped in, she's gone! There is no chance we could wait in a security line with her on the loose. You do have to get the child out of the stroller to get through the scanner but if you use a lightweight one it's no big deal. And people will help you. And it gives you somewhere to put any loose snacks, toys, whatever and hang your bag on too. You check the stroller right at the plane so you have it until the moment you walk on the plane, and get it back right after you exit the plane when you land. I'm not a leash person, and besides, my 2 year-old would throw herself on the floor at some point and I'd end up having to carry her anyway.
2) I have a portable dvd player for each child and have their favorite movies in a small dvd holder. Entertaining them with DVD players during the flight is easy - it's the time before the plane takes off and then the time before the landing when they tell you to turn everything off that can be hard. It can be 30-40 minutes from the time they tell you to turn off the DVD players until you get to walk off the plane. That's where the real planning comes into play. So when we first get on the plane, we read books and make a big deal about looking out the windows at the activity on the ground. Lots of planes and workers to look at. Then for the end of the flight, I always have special packs of surprise stickers that I save just for this moment. Also I bring the kids' Tag readers...the flight attendants never tell me to turn these off - and it saves us while the other kids are the flight are all melting down.
3) Pack lots of snacks. Dried fruit packs easily, popcorn, pretzels, granola bars (chewy kind so they don't break into oblivion in your bag). I bring a "cool pack" big enough to fit 2 sippy cups for the milk (don't assume they have it on the plane - in many cases they don't) and room for some string cheese. I use one of those ice packs you just refreeze to keep everything cool.
4) For ears - make sure both kids drink something during the ascent and descent. My 2 year old has no issues with her ears on flights; my 4 year old does. So stock lollipops and that should help the ears and make them happy too. I don't like giving either of them lollipops ever, so it's a huge treat and works like a charm. Also when the drink cart comes by I get them each a cup of ice. It's weird how long a cup of ice can entertain kids. They'll get a little wet - so what, it's just water. Ask for extra napkins when you get the ice.
5) Before your trip pick up some of those scented Arm & Hammer plastic bags - you can buy them in the baby department at Target - they have cute little dispensers for them that you can easily store in your carry-on. Assuming your 2 year-old isn't potty trained, if he does decide he just has to poop during the flight, you have somewhere to put the smelly diaper that will totally not smell once closed up. Let me tell you - you're not changing a 2 year-old in the airplane bathroom. I can barely pee in there comfortably! Plus, it's gross! You have to stealth change him on your seat when the flight attendants aren't looking (they don't like it). You probably know this, but they also sell disposable changing pads in the same area at Target - perfect for stealth airplane changes!.
Most importantly, try to just be as laid back as you can. If you are relaxed, it will go SO much smoother. Spoil them a little during the trip - after all, it's their vacation too. ;) Chances are, if you are having fun, the kids will have fun too.