Hi David, only just seen your thread.
As mum to 2 boys 13 and 8 I'd suggest that at WDS you make sure you see the Stunt Show, RnR if you're both into coasters, it's fast and Crush's coaster, although we haven't ridden it yet, going by reports it's probably not a bad idea to head straight for that one when you get in the park.
Armageddon and the Tram Tour if you're into special effects and Cinemagique, well worth it if you have time. Aladdin is similar to Dumbo and Orbitron in the main park but will probably have a shorter queue.
In the main park, I'd say your must do's are Phantom Manor and Big Thunder Mountain in Frontierland, Pirates of the Caribbean and possibly Indiana Jones dependent on your nephew's height, Buzz Lightyear, Star Tours, Space Mountain if you're both tall and brave enough, the Nautilus is well worth a walk through, Autopia and finally Orbitron (bit more oomph than Dumbo). Plus you have the Lion King show and Honey I shrunk the Audience in Discoveryland, both of which I think your nephew would enjoy.
Fantasyland - Pinnochio, Snow White, Peter Pan, Small World are all well worth riding, but wouldn't be my boys first choice if time was limited and you will have the parades and the Christmas season shows too. If your nephew isn't into the parades then it's a fabulous time to ride the attractions, but I'd recommend you try and catch the parades, perhaps on Day One you could hop over to the main park in the afternoon and watch them then.
I'm going to be honest and say I don't think you'll fit everything into 2 days, for me, the minimum I'd recommend is 2 days in the main park and 1 at WDS. Time really flies by when you're there. Use the Fastpasses as much as you can but be selective, you can't hold more than 1 for the same time slot, so if for instance BTM is a must do - make sure you head for the FP machines as soon as they open and then ride PM or the paddle steamer whilst you wait. Given your limited time I think it would be a good thing to have some plan of what you really want to do. Eat as much as you can at breakfast and then eat on the hoof during the day and have your main meal after the park's closed.
If you want to have a look at some maps, so you can get a feel for the place, I've got some, the entertainment schedule will be different, but you're quite welcome to them and I can pop them in the post for you.
I'm sure you'll both have a fabulous time, probably the first of many.