GS10 went to 4H camp just before he turned 9, and again this summer just before he turned 10. It was a mixed age group from 9 to about 14, with kids from 14-18 as student counselors and adults to supervise. It was also mixed gender, but of course they had separate sleeping quarters. In that situation the age differences were just not a problem. The adults should keep a lid on the boy/girl situations.