Pack all of your childrens complete outfits seperately in Ziploc bags, makes it a cinch if your husband is like mine and can't dress the kids without everything laid out! Just toss them the bag and they have everything. Also when you go in the parks you just grab a baggie each and they have a full change of clothes.
I would recommend Water Sandals instead of sneakers. Maybe
crocs as well. There are LOTS of places to get wet in the parks and I recommend letting your kids play in the water fountains at EPCOT, MK, etc. Also this way you aren't hauling around shoes and socks everywhere. Anything to lighten load is always good.
For snacks Disney Security is fine with you bringing small snacks in for your children and juice boxes. (I had one joke he wanted to hang out with us cause we had good food!) But Goldfish, Raisins, Pretzels, Popcorn, Peanut Butter Crackers etc are great and won't get gooey in your back pack. Again designate a Ziploc baggie per child! This way the boys could see how they were doing on snacks and tended to pace themselves. You can bring juice boxes but I recommend FLAVORED WATER. Juice contains sugar which will only help in dehydration, water is the best thing you can put in your child's body in the Florida sun. Flavored water was the only thing that worked for us, Grape and Strawberry.
If you have a Dollar Tree near by they sell 2 Glowsticks for a dollar. I bought enough for the entire family to wear the same color every night. This way if we were in crowds or on a dark ride my kids knew exactly where we were. Plus this cuts down on the amount of JUNK you end up hauling back home from the parks.
We gave our eldest a small flashlight that could clip on his clothes. He hates severe dark and some rides are VERY dark. So the small light was perfect b/c it didn't detract from the experience or hurt the ride, just eased him into the Haunted Mansion, Peter Pan, and POTC.
For passing time in the lines for attractions and ADRs I brought Bubbles. My kids and heck everybodies kids LOVE bubbles and it wasn't an odd occurence that this was an ice breaker and friend maker for my boys and other kids in the parks. I also brought little Magna Doodle pads, flashcards (small ones by Scholastic), Etch a Sketch (again small) and kept those in a Ziploc in the Backpack. So if we had to wait they had something to keep them entertained. The BUBBLES work though, never have seen anything like that. We had adults chasing them with their kids!
If you have a Big Lots near you they have Buzz Lightyear, Ariel and Tinkerbell light up fans. My boys loved theirs and kept them on them constantly! Plus, again a 3.50 investment here would have cost me 9 bucks there!
Depending on how old your eldest is give them a throw away camera to document their trip! It is really a neat view point to see the parks from a 4 year old perspective. I let mine play with the cheaper digital camera at home and we get some neat shots from him! It'll cost at the most $20 including developing and you can make it a cool project if the pictures turn out well!
To P/P:
The spritzer fan is a good idea! We bought our there but there are places on eBay that sell Disney merchandise right from the parks! Great to buy before you go. You may have a bag devoted to that stuff but it will end up saving you some money once you get there!
A plan or outline to your day. Most toddlers do well with SOME structure, not a bunch but some. So we would go on Snow White, but while we were waiting I would prep them by saying "After this we can go on Peter Pan, or the carousel. Which would you like to do?" This kept them in the decision making process (it's their trip too) and also kept us from running back and forth to different rides all over the park.
A word to the wise:
When all else fails just let your kids be kids. Towards the end of the first day we had done plenty of attractions but I am a ride nut and the kids wanted to play in the 100 acre wood. Eventually we calmed down and let them just run and play for a good 2 hours before Wishes! They had a blast and some of our best pics are from that area. It is really a cool play area for toddlers and younger children.