I think it's great that you want to help kids in the summer, and offer your services for free so that more children can benefit.
Here is an article on About.com, "How to Start a Summer Tutoring Business," which may have the insights you seek....
http://k6educators.about.com/b/2006/06/15/how-to-start-a-summer-tutoring-business.htm
You should also check with your city, county and state education regulatory agencies with regards to licensing and any requirements they may have for starting a tutoring program in your area. You might start with the U.S. Department of Education website (
www.ed.gov) for national regulations and materials they offer for tutors, as well as any state/local agencies they recommend you connect with to begin your program. Lastly, you might contact local tutoring businesses in your area and seek their advice or collaboration for your program (there may be potential customers who can't afford their services but would benefit from yours -- your program serving as a free supplement or alternative option to theirs).
Good luck with the endeavor -- I hope it goes well!