My son can now ride a bike and he learned on his own. I found this Youtube video on how parents should teach kids how to ride a bike in a fun, stress-free and untiring-for-the-parents way. Of course the parents or an adult still needs to explain how the kids should do it.
My son learned how to balance in an hour, how to do a U-turn in an hour. I am not kidding!
Here's the video: