Hellobee Boards

@babynumber1: We use a travel vest on all of our trips. It might work with your 4 year old but it's pricy. Still LO2 can use it when he/she gets older. And I'm assuming resale will be strong. Mine held up really well.
http://saferide4kids.com/product/ridesafer-travel-vest/

Maybe a dumb question, but will you have a car? You could always just bring your car to the park that day. You'd have to pay for parking, but it'd definitely get you out of there quickly.

What resort are you staying at? Could you take the monorail to get part of the way there instead of a bus the entire way?

Could you do the fireworks at a closer park (i.e., Epcot is walking distance from Beach/Yacht Clubs and has evening fireworks)