It's exciting to be planning your first (almost) trip to Disneyworld with your children. You will find that the World has changed quite a bit since your fifth grade trip!
Already some great websites for you to check out have been mentioned. Not sure if any of the below will be helpful to you, but just some thoughts as you embark on your planning.
--As you plan the trip it's easy to get overwhelmed. It's easy to feel stressed and to feel like you MUST see everything. This way of thinking can be the undoing of a vacation. Just my opinion but I find it's far better to take it slow and relaxed, set up a few fast passes per day, and not get weighed down by having to make table service dining reservations. Rarely does a day at Disney go exactly the way you plan. You have to be willing to veer of course a bit and be okay with it! After all, this won't be the last time you will visit the parks...anything you miss this trip you can prioritize for next time
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--Unless you are driving, my advice is the best way to go is to stay on property. Value resorts on site are a less expensive option. Staying on site you are able to use Disney's Magical Express transportation (a bus) to and from airport (included with reservation.) And while there you can use Disney's internal transportation (buses, boats, monorail).
--Everything is connected to a colorful bracelet called a Magicband that is provided when you make a reservation at an on property hotel. The band holds your park tickets, it's your room key, it is the way you pay for meals if on a dining plan. All you do is scan the ban. There's nothing to have to carry around anymore. Everyone in your family will get one.
--A 'parkhopper' pass is a ticket that allows you to move between parks each day (as opposed to a ticket for a single park per day.) A 'fast pass' is the term for Disney's line jumping for attractions. A fastpass gives you an hour long window to go to that attraction and jump the line. Everything about your trip can be to be set up on the 'My Disney Experience' website, as well as on the Disneyworld app. You can set up fast passes weeks in advance of your trip, right on the app. You are able to set up three fast passes for a single park per day.
--There are a couple dining plans available. These may (or may not) be advantageous to your family, you can check out some of the pros and cons reading through discussion threads etc. I always bring my own snacks there. I pack a couple of 10 packs of drink boxes in my suitcase, as well as granola bars etc. It makes the suitcase heavy, but it's worth it to me. Everything is expensive at Disney!
--There is nothing wrong with going 'old school' on the trip planning and visiting a travel agent that specializes in Disneyworld vacations.
Happy planning and enjoy your trip!