The Dyson Air Multiplier Bladeless Fan is interesting because it has no blades. It draws air into the fan and "multiplies" the speed up to 18 times. You can actually get pretty creative with its unique design.
Kids can be entertained by slipping different objects into the continuous air stream the fan produces where the blades would normally spin. But take it a step further and it could be used as part of a science experiment. If you drop a baseball through the middle of the running fan it's going to go all the way through with little change to its path. But what if you drop a feather onto it? The air currents created by the fan will push it to the side. A child could run an experiment to track which objects would fall through the middle of the fan when it is running and which would float to the side and not continue on through the hollow circle and to the floor.