Jenny,
I THINK the ships have a few loaner strollers. No car seats, though. You can get car seats, often for an extra charge, from the car rental places, unless you specify vans with the integrated seats. But my advice would be to bring your own, sad to say. Then you know how they work (don't forget extra buckles for the seatbelt locking) and you have them every step of the way. You'll have them on the way to the airport (or on the drive down), you'll have them to the port and you'll have them to stick sleepy kids in everywhere in the parks, to and from, and the ports. It is much easier to just store all the things in your room rather than worrying if you can get them. The ships are not hard to push a stroller around in. I've even done wheelchairs, so trust me on this. With the ages of your kids, it probably would be good to have a couple cheap umbrella type strollers (get the type with a flip-up sun shade) that could be ditched post-cruise. And if the kids have seats on the plane, you definitely want your own car-plane seats. They will check all the stuff right by the plane gateway, strollers AND seats, if the kids do not need them on the plane. I also thought my kids did better on planes if they were locked in a seat. Even babies get to know the rules! I know it sounds terrible to schlepp all the stuff, but better than transferring a sleeping child. And don't forget, when you use up all that space in the luggage that the disposable diapers took up, you'll have extra space for shopping!
Carla (glad my kids are now old enough now I don't have to deal with all that!)
Something disposable to drape the toilet area in the bathrooms is also handy. Changing a diaper or pull-up in a plane restroom can be a real challenge.
Nine Months to Go 
