The apparent levitation of the hovercraft is a simple, novel, way of engaging a child. There is very low friction between the hovercraft and the surface it floats on, and a few hours of fun can be gained just from seeing how it floats on different surfaces and inclines.
It should look like this:
Principles
The hovercraft's functionality is almost entirely derived from thrust. The force from the thrust approximately counteracts the weight of the object. A lot of the fun of the hovercraft however, comes from the lack of friction. If the power is user controllable, you could try to see what differences there are between keeping it floating on different materials and at different heights, and how stability is effected. The lack of friction also allows for inuitions to be built up about newton's laws.
Feasability
Cost is almost negligible, requiring a straw, something to produce a pressure difference to induce flow, and a foam plate. If the toy were to be manufactured, there would be other things (a housing for the pump, decals, paint), but it's a relatively low cost toy in terms of fabrication and materials.
The toy's durability largely relies on what the disk is made out of, and this is proportional to cost. The sturdier materials will be heavier, and require a stronger pump, which will cost more money.
The hovercraft will be a safe toy to play with, so long as the pump housing remains intact. I cannot imagine how someone would hurt themselves with a foam disk too large to swallow, and too soft to hit someone with, but I'm sure I would find out if this were actually mass produced. Given this, I would say the toy could be appropriate for ages 4 or 5 and up, or whenever the child stops instinctively gnawing on things put in front of it.
