Hi, Kristin!
You must be so happy to head back to Walt Disney World, especially with the littlest one who wasn't with you on your last trip!
Regarding earlier park closing, the answer depends on what you mean by "early" and which dates / parks you're considering. For example, on Tuesday, September 10, 2013, Magic Kingdom will close at 7 p.m. to regular Guests in order to make room for Mickey's Not-So-Scary Halloween Party, a special ticketed event; there will not be an additional showing of Wishes Nighttime Spectacular. Instead, Guests who attend MNSSHP will get to enjoy Happy HalloWishes. Take a look at this
link to a park hours calendar for more information.
Animal Kingdom's Picnic in the Park is not offered at this time. However, you'll find some great grab-and-go items available in some shops in the park. I noticed a small refrigerated case in a shop which included wrapped sandwiches among other quick items. Plus, at Harambe Fruit Market (right in front of Kilimanjaro Safaris) you'll find fresh fruit, carrots and celery sticks, soft pretzels and drinks that are easy to tote with you as you tour the park.
Can't miss attractions for your family? You'll have to visit
New Fantasyland in Magic Kingdom, being sure to book a Table Service dinner or grab a Quick Service lunch at Be Our Guest Restaurant. (YUM.) You'll find a different collection of characters in the parks, too, reflecting some of the most popular folks from the newest Disney classics as well.
Over at Disney's Hollywood Studios, Star Tours-The Adventures Continue will be great for anyone 40" or taller. (Similarly, if your 7-year-old is 44", you can head to Epcot's Mission Space this trip, too!)
Send another question with more details, Kristin; I'd love to help you plan!