You've got a wide range of ages but we can find magic for all of them! Involve all the kids in planning. Go thru the attraction descriptions on the website & let them decide on their "must dos". You may even have to divide up at some points. The crowds should be a little lighter for you during your visit b/c a lot of schools will be back in session during your vacation.
Let's start with MK. The older kids may like some of the bigger rides like Space Mtn, Splash Mtn & Big Thunder Mtn RR. The younger kids will love Fantasyland & Toontown. If the older kids don't want to ride those attractions, they can hop aboard the bigger rides & meet you at a designated place later. Visit Fantasyland first & ride Dumbo 1st as it gets more crowded as the day goes on. Everyone will love Buzz Lightyear's Space Ranger Spin. Be sure to see the parades & fireworks. You'll need to find a good location ~ an hour before time - may be more. I recommend sitting on the Main Street side of the Castle for the fireworks. Tinker Bell flies right over you.
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The Pirates League that is big fun (must be over 3). If you had to ask me to skip an attraction, I'd vote for Stitch's Great Escape. Its in the dark & can very scary for little ones. Great attractions to cool off, Country Bear Jamboree, Hall of Presidents & Carousel of Progress.
Your 180 day window to book ADRs is open & you should & do that. If you want a character meal in MK , check availability for the Crystal Palace or Cinderella's Royal Table. The Liberty Tree Tavern offers a family style meal & is all you can eat. I love that place. Running out of room again - sorry - please come back & lets discuss the other parks. Allison