D.C.
Some good stuff from other posters. I agree that if your child is going to their house, you go to their house for the interview.
My questions would include:
What kind of structure will you provide? Will my child have homework time? Or all open play time? Will my child play outside every day? What will you do with him when the weather is bad? What will they feed him for dinner? What is their policy on snacks (especially if they are at their house and not yours)?
There are no right or wrong answers to these questions. But these are things for you to think about too. Would you prefer your child get to run around and simply play after being in a structured classroom all day? But that means you have to proctor homework at night. Or would you prefer your child get his homework done, then a little playtime. And then when you get home you don't have to do homework with him.