We have a Gyrowheel for sale - we bought this up in the USA for our girl when she was learning to ride her bike. 

The original technology was developed and patented as Gyrowheel. The patent was then sold to Jyrobike which use it to make both the training wheel and the full bike. 

Basically you replace the front wheel in the bike with this and instead of using training wheels (which teach bad habits) kids learn to ride a bike with a little "science" help.

The wheel contains a rotating flywheel driven by a rechargeable-battery-powered motor that spins at high RPMs like a gyroscope. This flywheel spins significantly faster than the front wheel rolls and acts as a gyroscope, even when the bike is moving slowly, such as when the rider is starting. The flywheel causes the front wheel to respond to a lean by precessing, that is the front wheel turns toward the direction of the lean, which can help provide stability at low speeds, whether riding straight or turning.

In other words, even if the kid lose balance the bike won't fall, or will do it so slowly there's time to put feet on ground, or some other action. Just watch the video:



The wheel itself sell for GBP 119 now. We are asking $ 100 for it (comes with US charger, works on 220v). Add $20 for shipping outside Wellington.