Wow! We all love Disney! So many great responses.
My husband and I used to call it the Evil Empire because we thought it was all about the dollars. After going for the first time two years ago, though, we are hooked! My mom took my sister and me and our kids (7, 9, 9 & 12) last month. What a great place for an intergenerational vacation! Remember to check in with all age groups frequently - your mom and dad might not remember what it's really like to travel with kids in a crowded place.
We each had favorite rides, etc, but here are the hands-down faves agreed on by everybody in our multi-gen group: Disneyland - parade, fireworks, Fantasmic, the Peter Pan ride (We all went on it twice!), Tom Sawyer Island, the Star Wars Show. California Adventures - Muppets 3D, Soarin' Over California, the Brother Bear play area.
Originally, we didn't want to separate to do different things. But since we were only in each park for a day each, we did split up. My sister and I took the two adventurous kids on the thrill rides, while my mom took the two more timid kids to other attractions. That worked out well for using fast passes, and all the kids (young and old) got to do their number one choice in each park.
We had a great meal at the Mexican restaurant in the Frontierland area of Disneyland - healthy food for everyone at reasonable prices. Other than that, we did what everyone has suggested - BYOSnacks and water.
We stayed at the Desert Palms, too. Nice suite, and with a full kitchen we can bring our own dinner (like pre-made spaghetti sauce or lasagne).
On thing I'd do differently: My kids haven't seen some of the older Disney movies. They know the stories, but not the Disney versions. Next time, we'll rent them in the months before we go, so the kids are caught up with some theme rides, like Splash Mountain, Snow White, Alice in Wonderland, etc.
To skip: Finding Nemo (the wait isn't justified by the ride), Autopia (Again, the ride isn't all that fun unless you have a kid who is hopelessly in love with all things car. If so, make sure they have good upper body strength and can reach the pedals, or it'll be a bust. It's also smelly - think 300 lawn mower engines going full blast in the summer heat.)
One more note about traveling with varied generations - if anyone over stroller age has limited mobility (can't walk far), get to the park early and rent an electric scooter. Doing this made it possible for my mom to stay with us through both days, all day long. Disney also has a policy of helping families stay together, so they will do whatever it takes to get someone using a scooter or wheelchair on the rides with their group. The staffs' positive attitude and willingness to help made everything so easy.
Every time I think about that fun place I just feel all magical!