Hi Gillian,
The last time I was at Disney's Hollywood Studios, which was last month, you could meet Lightning McQueen and Mater at Luigi's Garage. When I called this morning, I was assured that they are still there. However, Disney reserves the right to change the
characters you can meet and greet at the Studios at any time. However, I've seen them there for years and with Cars 2 expected to be released in summer of 2011, my personal belief is they are not going anywhere anytime soon.
Be sure to pick up a "Times Guide" when you first enter the Studios. On the back there is a section titled "Characters Greetings"; look to see what time you can meet with the stars from Cars.
When my youngest was 3, his favorite park was the Magic Kingdom. He especially loved all of the attractions in Fantasyland, except for Snow White's Scary Adventures. He also loved the
Seas with Nemo and Friends at Epcot. He's 5 these days and he absolutely loves Finding Nemo - The Musical at the Animal Kingdom.
If your son is a Star Wars fan, be sure to watch the Jedi Training Academy over at the Studios. He might be too young to battle Darth Vader, but he'll probably enjoy watching the other children. My 5 year old loves watching, but is afraid to take on Darth Vader himself; he likes to watch his older brother fight with a light saber.
By the way, the Animal Kingdom Lodge is a great resort. It's my youngest son's absolute favorite resort. Waking up and seeing the animals right outside is a treat! Be sure to make a reservation at Boma. It's a great buffet restaurant; my youngest has never had a problem eating there and he is a very picky eater!
Have a magical vacation!