At my dojo, we are about half & half. The majority of my students are children (I teach beginners classes for a Youth Center on an Air Force Base). There is another martial arts instructor (Kempo) on the base who has more students, but most are boys. It seems parents prefer that their little girls learn how to defend themselves in a less competitive and violent (no punching or kicking as defensive techniques) manner.
Works for me, I've found the girls listen better than the boys and learn the technique names quicker. The girls don't try to muscle their way through a technique either, instead they focus on proper form.
Also, there is nothing cuter than a six-year-old girl tossing her twelve-year-old brother on his butt in Kotegaeshi
p.s. The dojo I visit on a semi-regular basis is about half & half as well, with more women yudansha than men.