A very successful program has been to provide field trips for the Girl and Boy Scouts of America. These field trips provide the children with the opportunity to earn badges.
Write a letter to the director of both the Boy Scouts of America and Girl Scouts of America explaining the program you have to offer (a special mini-camp for 2 hours).
Send the letter to area directors who then contact the individual groups (or if you know of a scout in your school you can contact the pack leader.
Check the web for a listing of fitness-related badges. Keep in mind, when working with the scouts, you have the opportunity for free advertising in your local paper.