Your plan of mornings (be there 30 minutes before park opening) with a break, then returning in the afternoon works great. You’ll tour the park when they are least crowded and avoid the hottest part of the day and your kids (and adults) will be rested if you want to stay for evening fireworks.
Another general suggestion (and you may already have done this) is to decide whether or not you want to do everything together as a group or split up at times. When I’ve traveled with my parents, they’ve taken time to sit on a bench for awhile or head back to the resort before the rest of the group. We eat meals and do most activities together, but there’s also some alone time for everyone. That works for us, but not all families, so it’s best to decide how to handle this before people start to get tired from running around the parks.
As for things to do:
Are character meets important? I just traveled with a friend’s family, including their 5 year old daughter, and we visited many attractions, but the character meets and autographs seemed to be our first priority. If that’s going to be the case with your children, then it’ll take some planning (we didn’t approach this very efficiently). Check out the schedules on Kenny the Pirate’s website (http://www.kennythepirate.com/), particularly for those who don’t have formal meets (like Town Square Mickey or Princess Fairytale Hall) and plan to arrive 10-15 minutes before the character is scheduled to appear (lines form very quickly and in many of the Epcot meets you may wait through a character’s scheduled break until they return).
A lot of people seem to overlook things for kids to do in Epcot. There are plenty of the aforementioned character meets and also kidcot activities around World Showcase (mostly coloring). Some families have prepared “passports” or other quests to encourage their children to visit each World Showcase country (and get the passport stamped or learn something in each country’s native language). There are kid-friendly activities inside Innoventions, that you can visit in late morning/early afternoon, when crowds build and you want to get out of the heat/rain. Many kids are fascinated by the aquarium at the Seas pavilion, in addition to the Nemo ride and Turtle Talk show. Soarin entertains people of all ages and if your kids meet the height requirement, then they’ll probably also enjoy Test Track.
The best of Animal Kingdom are the side trails, like the Maharajah Jungle Trek and the Pagani trail, but also the unmarked ones near the tree of life or in the Oasis as you enter the park. The Safari is usually fun and Everest is great if you enjoy roller coasters, but seeing the animals or carvings and talking with the guides is what the park does best. I’m also a fan of all three big shows - Lion King, Nemo, and Flights of Wonder. It is, however, a tough walking park, so I’ll usually leave just after lunch and “hop” to another park for dinner.
The kid-friendly activities in the Studios are probably obvious, with the Disney Junior show and character meets in the animation building. If the Frozen singalong is still going on, then I’m guessing that’ll be on your list, too. I suspect you already know what you want to see again in Magic Kingdom and what you missed, so I won’t add much there. If you have time for Tom Sawyer Island, though, then try it out. Your parents can sit on the porch and rest while you run around the island with the kids. A trip of the riverboat can work the same way, with the kids exploring each deck with one parent, while the rest of the group sits down and enjoys the ride.
Spring Break should be a great time to visit the pools. The summer heat and humidity shouldn’t have arrived yet, but it’ll probably be hot and sunny in the early afternoon when you return for your breaks a swim/nap should refresh everyone for the evening.
Take the bus to Downtown Disney. I like to drive most places on Disney property, but with the current construction parking is a mess. That may change, but unless you hear otherwise, plan not to drive there right now.
