Not that I'm advocating dangerous play or anything: This is probably not good fun for a preschooler. But, by the time they can safely ride a bike they have probably learned that revolving things aren't safe for their fingers.
So with that in mind, here's our list: Stand over the uptilted fan and act like the Stay-puff Marshmallow Man; put your face near the fan and use the "Turbo Fan" voice; blow streamers out into the room and let your siblings run through them; and lastly, use the fan for cooling off when it's super hot outside. If the temperature reaches 70 during the day, you probably should use a fan to prevent heat stroke. It's just a good safety precaution, you know.