My children (12 and 16) are fluent (more or less) in three languages each and can get by in another one or two. If you want your child to learn, put him in a regular camp in France. Make a point to ask that they _never_ speak English with him. You can find a list of French camps here: http://tinyurl.com/apyw9
This is not a definitive list, just something I picked up quickly. As I child/youth I spent time in other countries and usually left fairly fluent provided people only spoke to me in their language. I think you would make a mistake to look for a camp "good for non-native speakers."