Hi Carrie

and welcome!
This is our first trip to WDW too -- we go to DL about once a year, but wow, WDW is something else entirely! I was overwhelmed when I started, but once you start planning, things start falling into place like pieces of a puzzle. Things you need to consider:
When are you going? Will it be really crowded, slow season? If it's really hot you may need some mid-day breaks, or plan your sit down meal at lunch time when you can get indoors in air conditioning.
Are your kids boys, girls? Do they -- especially the little one -- have any favorite characters? Are the teens excited about planning the trip, or rolling their eyes
Will the teens be with you the whole time, or are they likely to go do their own thing and meet you later? Can your little one keep up with everyone else with no nap or rest time at the hotel? Is the little one tall enough -- and brave enough -- for the thrill rides?
What resort are you staying at? Are you spending the whole time at Disney, or going anywhere else? How long is your stay?
Are you doing the Dining Plan (I guess so, since this is the Dining Plan thread)? If your family likes one sit down TS meal every day, then the Dining Plan is often a good option.
Are your family big eaters, light eaters, picky eaters? Want to try new things, or meat and potatoes folks?
Figure out park hours first, especially if you want to take advantage of EMH (Extra Magic Hours, when certain parks are open early or late). Then try to plan your day mostly around
that park -- meals, shows, etc. When I first started planning, I picked restaurants I thought DH and I would enjoy, without looking at the maps -- big mistake! We would have been running around WDW like chickens with our heads cut off!

So I switched things around to try to stay in one, or a the most two, parks per day, not running back and forth. For each park you are visiting, try asking each family member one or two things they want to see or do most of all, and plan to try to get those activities in for sure.
For example, for a day at Epcot: 5 year old loves Nemo. One teen wants to ride Mission:Space. One teen wants to see Illuminations. Dad wants to ride Test Track and Soarin'. And you want to eat at Le Cellier. So you might plan -- early morning at Future World, so everyone can ride Mission:Space, Test Track, Soarin', and The Seas with Nemo and Friends. CS lunch. Walk around World Showcase all afternoon (make sure to get the Kidcot Passport for the 5 year old to get stamped and signed), teens can head back to more rides at Future World if they want. Everyone meets at Le Cellier at 6 pm for dinner, Illuminations at 9 pm.
And it's very flexible -- if your 5 year old is a DD who loves princesses, and the teens can't stand them, then you and DD could have a Princess Breakfast at Akershus, while dad and the teens have a CS breakfast in Future World and ride the rides; meet them in FW after your breakfast. If you split up this way, you may end up having to pay for a meal or two later in the trip OOP, but it all works out. Planning is half the fun!
