Magnet Wheels

Principle: Learn what objects, materials, and surfaces are magnetic or ferrous by seeing what surfaces the cars can stick to and roll along. 

Interaction: Children can place the car on a magnetic or ferrous surface such as a steel car body, refrigerator, railing, or steel tub. This allows the car to stick to horizontal or inverted surfaces for an added layer of fun on the traditional "hot wheels" concept. 

Construction: Would have small metal axles and a plastic molded car body with a small disc magnet inserted into the bottom.

Cost: Essentially the cost of a small toy car + the cost of a magnet. Could contract manufacturing out to an injection molding business. Probably sells for ~$2 a car depending on size and model. 

Durability: Very durable. Would be made of molded plastic which would stand up to drops and crashes.

Safety: Magnet is not strong enough to cause any harm and is not removable. Would only be recommended for ages 3+ to avoid choking since the cars are small.

Learned: Kids like almost anything with magnets because it is an unusual phenomenon. I had lots of them as a kid just to play with.