Hey Stefan...haven't heard from you in a while. I have taken a small group of 10 year olds for 5 - 2 hour sessions of photography. I think the thing to remember is to keep it simple, fun, and activity based rather than theory based.
Try to get a sponsorship from a local camera store or one of the camera manufacturers to supply you with a heap of those disposable cameras - with a deal to have the films processed at a really reduced rate. Explain that for every $20 camera they supply, they have the potential to foster a $400 - $10,000 camera sale in years to come.
The children are really keen to just take photographs. I started by very simple instructions that if they wanted clear images, they needed to keep the camera still, and showed them how to. Instructions were then given on using the particular cameras they were provided with. A short question session on what they thought made good photographs...followed by sending them off to take photos.
The images were processed and examined - with a sharing time and short discussion examining examples of their photographs illustrating exposure, focus and composition. Then each week we concentrated on a theme - people, landscapes, action. Collating an album along the way was an important part.
I steered away from all compositional guidelines and let their own creativity and experimentation guide them. They themselves came to know which images worked for them.
We were lucky and had cameras and processing donated, and time between each lesson for processing of film. A bit archaic in this age of digital, but cheap and easy to administer in this school setting.
If you want to do digital, most families have digital cameras, but standardising instructions for the myriad of cameras brought may be a problem - and if you don't know how to operate Johnny's dad's complicated camera, it could take your time away from actually teaching and supervising the children.
Doing a photography course where the children don't get to hold photographs can be a very empty experience. They just love passing images around and giggling, putting them on pinboards, and scrapbooks. Looking at them on a screen just doesn't have the same impact with this age group....so if you go digital..you will also need someone at the camp to take care of all the CF cards, download all the images, and print out all the pics after every session. It could be very time consuming for someone. You could perhaps outsource this if there is a local lab nearby the camp, giving the members of the camp a flyer mentioning the lab's sponsorship.
Just a few ideas. It is so much fun with the children - they have endless enthusiasm and creativity. Hope this helps a bit.