I agree w/ Shannon H., charging a small entrance fee for like $5 for each kid that can walk and also have cafeteria that you can charge a bit higher price to make more profit, selling anything from juice, coffee, cupcakes, wipes, diapers.... Kind of like chuckie cheese. We so need places like this around here, 'cause sometimes outdoor public playground just so dirty and i even see people smoking around there, which is not healthy at all. No need anything fancy, just playground equipment w/ cushion floor, you know, the rubber floor kind. For party, i would say rental the place for $150 for first 2 hours, then $50 for each additional hour, schedule ahead of time of course. You can have people bring their own food for the birthday party, or you can also cater for them.
Good luck w/ everything and keep us posted once you have it open!!!