First and foremost find out how much the trip is going to cost - hotel, plane, tickets into WDW, etc. Once you have a rough idea of how much you need find ways to do it. Your kids will help to if their into Disneyworld too - rent a movie vs. going to the movies, give them the option of toy now or Disneyworld if we save it, etc. Also:
#1 - and easiest of course is the change thing.
#2 - I found that if you get extra cash - ie: bonuses, incentives, rebates buy Disney $$$ with them because its a lot harder to spend that
#3 - If you bring lunch to work, don't eat out, don't get that coffee in the morning designate a jar or add that money to the change jar.
#4 - In MA we return cans. .05 per soda/pop can. If you can do that it's amazing how fast can money adds up. Usually I'm around $10.00 per trip. If you have a small office that you work in and no one there saves them see if your boss would mind if you put a trash can to collect there - most people pitch them into trash when finished at work.
#5 - Make a rule for yourself and the kids - swears, tantrums, any undesirable behavior you have to pay the jar - ie: .25 for a swear. If you have chores for the kids and they don't do them $1.00 of allowance into the jar. You could also have their own separate containers for them to save their own spending cash and save with these same ideas.
Good luck and have fun!!!