My husband and I flew with both of our kids for the first time (we flew with our oldest a couple of times as an infant but this was the youngest's first flight) from Kansas City to Portland, Oregon back in September. The logistics of the airports and flights with the kids certainly wasn't what I would call fun - plus the youngest, who was about 1.5 years old at the time had crazy diarrhea the whole weekend and also got carsick AND had a diaper blowout in the rental car - but we're still planning to take both kids to DLR this December, so I guess we weren't completely scarred by the experience! Here are my tips for surviving:
1. Yes to either carseat or CARES harness on the plane, for two reasons. First, holding a kid that age on a flight more than 30 minutes is going to be uncomfortable and maybe impossible, since kids that age don't want to sit still and will likely want to explore everything on the plane. Second, the safety risk is just too much for us to ever justify trying to save the money or hassle of getting a separate ticket for each kid and bringing a car seat on the plane, and when I was researching travel trips for the first time we flew with our oldest, I found lots of stories from flight attendants and safety experts about how babies and small children can easily be injured with even minor to moderate turbulence. My cousin's 5 year old son was killed in a head-on collision a few years ago and her 2 year old daughter broke her neck but recovered, so I am vigilante about travel safety now...
2. I agree with other posters that I would never trust a seat provided or installed by a rental car company, for lots of reasons. So if you're taking a hired car service or rental car from the airport, it's a good idea to bring your own seat. The CARES harness makes more sense to me if you're taking one of the huge shuttle buses, since you can't use the carseat on the bus anyway.
3. If you do take a carseat on the plane, I agree again with other posters that either a lightweight carseat (that obviously still works for your kiddo's height and weight range) purchased specifically for traveling, or one of those rolling cart/frame things will be really helpful. We have Diono Radian RXTs for both kids, and while they are fairly narrow and fold up relatively flat, they are HEAVY and it was not fun juggling both kids, a diaper bag, another carry-on bag, purse/wallet/tickets and the two car seats. I did buy the straps to carry the seats like backpacks, which helped some but it still sort of sucked. We flew on Southwest, so I also decided to pay an extra $40 at the gate each way to get a boarding pass in the A1-15 range (I think I was like A6-7 each time), then I got on early with both carseats and the diaper bag and my husband hung back and boarded with the kids later. I got the seats buckled in so they were ready for the kids when they boarded, which worked out really well and we weren't blocking the aisles and slowing down boarding. I think we will still take the Radians on the DLR trip, but I plan on buying one of the carts so I can just wheel them right down the aisle of the plane instead of lugging them around on my back.
4. We did choose to sit at the back of the plane, for many reasons. We were closer to the bathrooms and could pop in faster if we needed to deal with a potty break or diaper change, it was a tiny bit louder and thus the inevitable tantrums and whining were drowned out a little, we weren't clogging up the boarding process as we tried to get the kids and all our stuff settled in/under/above our seats. Plus, with all that stuff and both kids there was no way we were going to be able to pop up and run right off the plane as soon as it pulled up to the gate, so we didn't need to be at the front to deplane faster. By the time we got everything packed up and ready, it was our turn to go - and we were in the last two rows on our side of the plane.
5. I know you were asking mostly about carseats, but don't forget to buy a few new toys and books before the trip and keep them packed away in the diaper bag until you're on the plane. That should keep him entertained for about 10 minutes : ) We also loaded a few movies on the iPad and bought kid-sized headphones, which did help keep them entertained. And yes, having some snacks and drinks on hand is important. I just brought two empty sippy cups in my purse and then bought water or juice after we went through security and filled them up, or the flight attendant may sneak you a juice or water before takeoff if you ask nicely. We use Contigo water bottles that I found at Target for $10 each. We have had a lot of problems with sippy cups of various brands having some strange suction/pressure issue that causes liquids to get sucked up into the straw on their own and spill out through the top, which would obviously be a mess when traveling. We take the Contigo ones with us everywhere and have never had a problem. Oh, and you might want to take a set of toddler/kids silverware in a ziploc bag, just in case, as well as wet wipes and/or napkins/paper towels for cleanups if necessary.
6. When we go anywhere with the kids, I take my Overland Equipment purse that has lots of room inside as well as pockets on the outsides by the straps that will hold a water bottle or umbrella. I have a smaller one that I used on a WDW anniversary trip without kids last January (I think it's the Donner style) that I have had since college, but my newer one is bigger and can just be thrown in the washer if it gets really dirty (style is called Belvedere - you can find most Overland styles on
Amazon or at outdoor/camping/bike shops). Even with the diaper bag and my oldest having his own backpack to carry his toys and snacks on the plan, it is nice having the extra room, and I carry it cross-body and fairly close so it's not sliding down my arm all the time like a shoulder bag would.
7. I think we have lucked out and have only had to change a diaper once on a plane, and it was just a wet diaper and the plane had the changing table, so I can't help you with the poopy diaper on a plane question. When our oldest was about 6 months old he had a huge blowout right as we were landing, the flight was super late already and we were about to miss our connecting flight, so my MIL and I ran off the plane as soon as it stopped and changed him in a bathroom at O'Hare, then we all ran to the departing gate. If it's just a wet diaper and we're fairly close to landing, I just wait and change it at the airport. Luckily the youngest's poop issues from our most recent trip had cleared up by the time we flew home, but I honestly don't know what we would have done if he had another blowout on the plane, even if there was a changing table. Since our oldest is now out of diapers and the youngest just started potty training, I'm now more worried about them needing to go on the plane when both bathrooms are occupied and having an accident, since there won't be a diaper to absorb the mess...
Don't worry, both of our kids are awful travelers too - the youngest gets carsick all the time - so you're not alone! Plus even if something ridiculous happens, it will make for a funny story later. I know it can be stressful traveling with kids, but if I have to endure a few hours of it in order to get to Disney, hey, I'll take it!