have you thought about packing and taking souvenir type items for your smaller children? You mentioned on your other post that they like candy. Buying some specialty/fun candy before the trip would save some money.
Disney Store sometimes has some good bargains on Adult and Kid t-shirts.
You could keep it secret and carry it in a bag and give it to them at the parks.
Or perhaps buy Disney items locally, and have some sort of gift bags with different Disney treats ready for them in the morning before you hit the parks.
Disney Stickers, Tshirt, Candy, Autograph books and Disney pens,
They will probably want the glow in the dark souvenirs when they see the other kids that have them at night. What about bringing some 'glow sticks' or other fun glow in the dark items along, but make it a surprise for them (or put in the above mentioned gift bags.)
The souvenirs at the park curbside kiosks are designed for impulse buys.
oops gotta go.