Heather,
Five is such a great age for a first trip! I am sure you will both love it!
As you can imagine, the longer you can go, the better. But that is not always in everyone's financial budget or friendly to their work schedule. So let me suggest it in two ways;
Option 1: The Ideal TripWith a little one, a trip can actually go on too long. So I would say that a schedule that allowed you a day each at
Epcot,
Disney's Hollywood Studios, and
Disney's Animal Kingdom Theme Park, and 2 days at the
Magic Kingdom would be perfect. Even better if you had an added day for pool and relaxation time in the middle of it all. That would make it a 6 day trip, not including arrival and departure considerations. With some good direct flights from the Indianapolis International Airport, you could arrive early enough and depart late enough to keep the trip to just 6 days, with park visits on both those travel days.
Option 2: Controlled Magic TripThose 6 to 8 day vacations don't always work out for us, so we sometimes will go with a shorter plan. We still fit in a no-park day, but we go to Epcot on our arrival day, and combine a half day at the Animal Kingdom with a half day at the Magic Kingdom. After another full day for the Magic Kingdom, and one for the Hollywood Studios on our departure day before an evening flight home, and we get it all done in 5 days.
With your little guy, I would suggest you could even skip Epcot to get more time in at the Magic Kingdom, and amend your trip as follows;
Arrival Day: Hollywood Studios
Day 2: Magic Kingdom
Day 3: Pool day
Day 4: Magic Kingdom
Departure Day: Animal Kingdom
As for making the trip better, you are already taking him to Walt Disney World. That is special in itself. I would not worry too much about 'plussing up' the trip. But certainly a few fun meals, especially for dinner on your pool day, would be a great idea.
Write this Hoosier back if you have more questions!
Have a Magical Vacation!