Knitting has a very steep learning curve at the beginning, but once you master the basics, a wide vista of possibilities opens up before you.
From the Lazy Genius, who is still struggling up that learning curve, some hints for the beginning knitter. All her hints are spot on, although in the first one she means circular needles, which I personally have never mastered--I prefer to use one very long pair of straight needles (from dowels three feet long), or a larger number of shorter straight needles for wide projects.
Children around the age of six or seven can have good enough motor skills (and perseverance, which is vital) to learn to knit. As my friend said, "The best way to learn to do a new craft is to read a book for teaching children how to do it," because a craft book targeted at children has to stick closely to the true essentials of the technique.