Any ad for any unicorn toy that has ever existed inevitably shows most (if not all) of the kids playing with it, being girls. The unicorn appears to be considered associated with femininity for some reason, despite the fact it's a fictional creature based upon horses, and despite the fact that horses have been used by men in the cavalry divisions of armies as a means of literally "riding into battle" (as well as men in many other professions in the past, including mail delivery, and also just as a normal means of transportation either directly or by pulling carriages for people of both sexes). But despite this, the unicorn seems to be inexorably linked with the female gender.
Can someone here explain why this is?
Other animals that seem to fit this "female only" stereotype are ponies (not horses in general, but specifically ponies), and also seahorses (albeit ponies and seahorses actually do exist).
Can someone explain to me why these other animals also are associated with femininity?