I'm late to the thread, but we've been to Disney World 6 times since 2017 and once to Disneyland in there, so I'm going to throw in a few things that I haven't seen posted by anyone else that are a bit off the beaten path.
1) Make sure the hotel staff knows it's your kids first trip. They'll get a button saying so at check-in and the odds of some "Disney Magic" happening increase significantly. My girls have had Tiana "visit" their room at Port Orleans while we were away and leave them some dolls and goodies and had the same thing happen at the Disneyland Hotel with a stuffed Olaf, candy, and a Frozen book.
2) When you need to take a break without taking a break, go watch the Carousel of Progress in Tomorrowland. Dark theater, show is probably 20 minutes long, I have taken several high quality naps in there.
3) As of April 2022, watching the fireworks at night is godawful. They line everyone up in rows in front of the castle and if you have kids, you have to either pick them up, or they miss half the show cuz they can't see. You feel like you're a stormtrooper watching General Hux declare the activation of Starkiller Base. If you want a really cool experience that we found out by accident, go ride the PeopleMover during the fireworks. You get all these great views of the castle and you are outside for probably 80% of the ride, you'll see a good portion of the show while sitting down and not being crushed in a mosh pit.
4) Get on a Facebook group and talk to other people who are going to be there at the same time and you can add all of your names to the PhotoPass thing, split the cost, and get all those great photos they take of you when you are on rides and so forth. It's just like splicing the wire to have everyone share the cable bill at the dorms back in the day.
5) Don't buy any souveneirs until you are walking out of the park. Don't be the idiot stuck holding a balloon for 6 hours because your kid wanted it at 10 a.m.
6) Find a place to sit on the curb and watch the big parade at Magic Kingdom. Your kids are at the age where having Goofy wave at them and Cinderella blow them a kiss is going to be the whole world to them. Ditto with meeting the princesses. I'd stand in line for a whole day to be able to re-witness my kids' reaction at 5 years old to seeing Ana and Elsa.
7) Don't go on the ride in the Mexico temple at Epcot unless you need to take a nap. It's outdated and not working properly. We got off of it when my daughters were 6 and one of them said, "Um, what was the point of that?"
8) If you go on the Tomorrowland Speedway, get ready to ingest as many carcogenics as if you had just chain smoked for 9 years.
9) When you get on the shuttle of Rise of the Resistance, go straight to the back window and claim that space. It's an incredible view of what's going on "outside" and you get the first look at the Star Destroyer that pulls you into the bay.
10) Sit in the right-hand pilot seat on Smuggler's Run, because that person gets to pull the lever to send the Falcon into hyperspace, and that is the thing you've been waiting for your whole life.
11) Soarin' always has one of the longest lines at Epcot, so here's what you do. Book a breakfast at the Garden Grill (cool rotating restaurant) before the park opens. You go stuff your face with food and then you walk down and you're the first people in line for Soarin' because the park hasn't opened yet.
12) Get or find an app of the Hidden Mickeys that exist all around the parks. Your kids will LOVE finding them.