Hi Eyla!
A first trip to the Walt Disney World Resort can be overwhelming. I have a 5 year old myself and he loves all of the parks, though his favorite is the Magic Kingdom, followed by Hollywood Studios, Epcot, and then Animal Kingdom.
First, I recommend ordering the free Walt Disney World
planning DVD. Then I recommend buying the book "The Complete Walt Disney World" by Julie and Mike Neal. It is a great book for first timers and it is full of color photos; it will help you to determine what interests you and your 5 year old the most. It can also help you in selecting restaurants to try..
You can get more information on the dining plans
here. The Deluxe Dining Plan is a lot of food! I usually don't recommend it for first time visitors because eating a lot of meals in a Table Service (full service) restaurant takes away time from seeing attractions. When I'm planning for my family, I usually plan on each Table Service meal taking between 60 and 90 minutes. I usually recommend that first timers only have one Table Service meal each day; thus you might consider the standard Disney Dining Plan.
Once you know when you are coming and for how many days, you can make a plan for which parks you will visit on which days. That should help you making dining reservations, which are critical for Table Service restaurants. A common mistake made by first time visitors is not making dining reservations before leaving home. With a 5 year old, you should consider some Character Dining Experiences. My sons absolutely love Chef Mickey's in the Contemporary Resort.
Hopefully this will get you started. Write back if you have any more questions!