Hi again Nancy! If you want to visit a park on your arrival day, then I would suggest the Magic Kingdom, as it is open the latest of the parks, until 10 pm on September 15. If you have enough time, you might want to skip a theme park on your first day. You can spend some time exploring your resort and maybe enjoying the pool for a bit. Then I recommend heading to
Downtown Disney. This is a first day tradition for us, and my daughter loves it! Coming from Ontario, we usually have late afternoon arrivals, and feel it's too rushed to head to a park.
There's so much to do at Downtown Disney, and it totally gets us in a Disney frame of mind! There are fantastic restaurants, both quick and full service, and shops for everyone, even eight year old boys! He can make Lego creations at the Lego Imagination Center, check out all the latest toys at Once Upon A Toy or make a car at Ridemakrz. And since he'll be starting pin trading, you'll have to be sure to check out Disney Pin Traders.
Hope this helps Nancy! Write back with any other questions!