So the way it worked when I was growing up 20 years ago was this -  children (8-12ish I think) were cub / tiger scouts and those typically had a den mother aka female leader. after that (12-18) you were a boyscout and we always had a male leader. I guess it was traditionally the switch from children with their mother to young men being led by a father. I can see it being important to have men for the 12-18 since they go on a lot of campouts / outings, but for children it doesn't matter much since they are just doing crafts / etc in someone's home. Just my experience.