My 6 year old saw one of his friend doing 1 finger knitting (I guess it's more like crochet) but he will sit for HOURS and make chains of stitches.  I bought him a cord of twine and he happily sits in the back sit, finger knitting and chatting with me during carpool.  He's made "lassos" and belts and bracelets. 

Now he's asking to learn multiple fingers so he can "make something".

It's so easy to learn and cheap!