I would bring out the toys and set up the room as you would have it when you have kids there. It's really hard for parents to visualize how you would set things up. For instance, my last interview I had had the day off, so my house was spotless and the toys picked up and put away. I could tell mom seemed unsure about that- and I've been in business for over 10 years, have had several of her co-workers as clients, and am always full. Now because of those factors I was able to reassure her, but if you are just starting out I can see the parents being unsure.
You say your home is older - is there a musty odor throughout, or just in the basement? Do you have a dehumidifier running? Not to offend, but how does your home look when you pull up? Is it well maintained with nice landscaping? Or is there peeling paint, sagging porches, missing shutters, etc? If there were obvious maintenance issues, I would be hesitant to enroll my kids because it might mean the provider won't have the money to provide the appropriate environment, toys, food, etc. With any business it does take money to make money...
Hope your other interviews go well and you get some kids!