A trip to a Disney theme park with the family is one of those occasions when you know you're going to take a lot of photos. If you don't have a camera that can switch out lenses, then just bring your compact point and shoot and count yourself lucky that there's one less thing you'll have to lug around. But if you want to bring your "big" camera with more than one lens, then there are a couple of things to keep in mind when you're considering which lens (or lenses) to bring.
Versatility
Walking around the park, you're going to face all sorts of photo moments. Sometimes you're going to want to try to get a wide shot of Sleeping Beauty's castle, and sometimes you're going to want a close-up portrait of your kid on the carousel. So a good, versatile zoom lens is the lens that you'll be using the most at the park. I use a Canon 24-70mm, and with the 1.6x crop factor (due to the sensor size on my camera) I get an effective focal length of 38-112mm which covers a great range of shots. You might be tempted to rent something big and crazy like a 70-200mm lens, which might be fun but is kind of overkill. At Disneyland, and Disney World I'm assuming, there aren't that many moments where you are going to want to take a really long shot. And you'll likely find that 70mm isn't nearly wide enough in many situations (I have enough problems at 24mm).
Fast Glass
"Fast Glass" is just a nerdy thing photography people say to describe a lens that has a wide aperture. A wide aperture lets in more light, and more light means the shutter speed can remain "fast" even in low light situations. At Disneyland, this is essential, especially if you're taking pictures of your kids. You're going to take plenty of pictures outside during the day, but you're also going to take plenty of pictures inside (restaurant, rides etc.) not to mention at night. Having a lens that will allow you to avoid using the pop up flash - or bringing an external flash - is awesome. I always bring my favorite Canon 50mm f/1.4 lens, and when we're watching the parade at night or I want to take pictures of my girls in "It's A Small World," the 50mm always delivers.
Other Disney DSLR Things To Consider
Don't bother trying to bring a tripod unless you really want to lug that thing around all day. You can try a beanbag or something like that, but honestly there aren't many places you're going to want to use one. I don't even bother with my Joby Gorillapod - it's just too annoying. If you're concerned about getting pictures of the whole family (including you) avail yourself of the many Disney Photo Pass photographers. They know how to handle your camera - just be smarter than I was and make sure auto focus is turned on.
Get a good camera strap that is comfortable and ditch that strap that came with your camera. Those straps are uncomfortable and all they do is advertise to thieves that you're walking around with an expensive camera. I've used affordable, normal straps from Op/Tech and like them, and now I'm using a shoulder strap from Black Rapid that I really, really love.
Use the smallest camera bag possible, but still bring a bag. I use an older version of this bag from Tamrac. It fits my camera body with my zoom lens attached, and there's enough room at the bottom for my 50mm. I also bought a water bottle attachment for the side, and I ditched the water bottle and use the attachment to hold my drink, my kid's water or whatever else I need to throw in there in a pinch.
Oh, and make sure you bring twice the memory cards you'll think you'll need (on the trip, not necessarily to the park) and a backup battery. Trust me. The real work comes when you get home and have to go through all the pictures you've taken.
RELATED POSTS (from Chris Ford):
Tips for Surviving a Weekend at Disney (with the Kids) [Man of the House.com]