Our tendancy is to see WDW as a whole. While some rides, such as most fastpass attractions are a priority, mostly we see variety as the priority. We aren't nutso about trying to do EVERY attraction, but we more or less try to go on each thing once, and everyone knows that's the game plan. If we get to an attractionand the line is very long, we know to skip it and come back. I'd never promise a child that we were going to go on ride X first thing this morning; ride X may very well be shut down this morning or have a VERY long line. I think using that mentality prevents anyone from saying we didn't do 'their' ride, or did 'their' ride second. It's all good, and we've having fun.
Conversely, realize that you can't see EVERYTHING. That's okay, you can plana second visit in the future and see it then. Like we may not see CoP on every visit, but when we do see it, we enjoy it. Part of what makes WDW fun is that every visit is slightly different. For example, there's about 80 different table service restaurants alone, not counting poolside dining or bars It would take you nearly a month to eat at each place just once. Then I think it would probably take another month or so to eat each quick serve place once. It would take you over two weeks to spend just one night in each Disney resort.
You can easily happen by an aquarium at feeding time, catch Leota blinking, greet a character you've never seen before, and so much more. So we really try to avoid the mentality having a list of must dos, and more have a very soft list of higher priority attractions, lower priority attractions, and a few attractions we mostly skip. Though we do talk about our favorites between trips.
It sounds like you kids will mostly be tall enough to go on most of the attractions, though they may be too scared. If you are going to split up for that purpose, it doesn't mean the only options for the little ones is to sit and do nothing. It may be helpful for them to have quiet time, but equally Disney also often provides secondary entertainment. Near BTMRR/Splash MTn is a little playground. Characters often appear near there. There's penny press machines to scout, gift shops, ride photos to peek at, restrooms, snacks, parades or singers, interesting birds, little theming details, fountains, beautiful landscaping, other guests.