Let us put skateboarding aside for a second and consider hover craft designs, hover boards prototypes and the reality of the forces of nature that they must deal with to perform. Let's explore both on planet and off planet activity for a moment to fully grasp what is going on.
One of the biggest considerations of hoverboard for kids will be the need for a very efficient propulsion system which is low-weight and powerful enough to over come issues with air-resistance as speeds increase. Hoverboards which are used on Earth will most likely have speeds of up to 45 miles per hour or less due to hyperbolic coefficient of drag curves as speeds increase. Since these technologies will be used where the air is most thick near the ground this makes sense.
If these technologies are to be used on other planets they may be able to propel the rider or a robot at much greater speeds without dealing with the thickened atmosphere and yet still this provides yet another consideration, the hover craft or hover board must work harder to lift the weight provided the planet is similar in gravity. If less gravity, one could design a hover board planet surface rover type exploratory device that would be quite efficient indeed.
Now let's get back to Earth and remember our goal is to propel a 90 to 160 pound kid around at a pace, speed and maneuverability that is desired by a human in their prime of life period of athletic ability and agility. That is what we are really talking about and we must remember that we have somewhat fixed challenges to over come here on Earth.
What sort of propulsion device do you think would work best for a Hoverboard? The Online Think Tank has floated many potential propulsion devices and some are not hoverboard for kids so far out of this world and are worthy of further exploration.