Also chiming in to say PLEASE don't offer a free week! (If you think about it, factoring for food/crafts, etc you are basically paying them!)
I would be worried about the people you will attract. The ones whose primary concern is how much you will be costing them. In the long run, you DO NOT want them!!
I like the idea of offering something a little different or unique, to get people's attention. It can be very frustrating or scary, but you will fill those spots, with the families you WANT to work with.
Fingers crossed for you!