My club offers 3 hour archery courses through the local Community Services District 8 times a year, that I lead. Each course is 15 kids from about 8-14, and they are always sold out. I try to get 2 additional volunteers from our club to help with each class, which almost always happens. I think you need a minimum of myself and one other person looking over things, or it's just not safe with 5 kids shooting arrows at the same time. Three is optimal. Our course and safety procedures are based on the booklet "Archery Instructor Training," by USA Archery, which you should get even if you don't take the course.
It is a great pleasure for me to do this, and the kids seem to enjoy it. If you would like to correspond with me, please do.