The five year old daughter of my LYS can knit. She started when she was four. Her mom has taught her things like you are always sitting with knitting needles. If you must move to a new location the knitting needles go in the knitting bag, you get up and move. Once situated you can take them back out again.
Remember knitting hasn't always been a luxury as it is now. Children had to learn these things too survive. I watched a documentary once that started how at one time a little girl was expected to have all the blocks pieced together before her fifth birthday. At the time a child living to the age of five was a huge thing so there was always a celebration and her blocks were on display. Yes I think that is a little much but our children are capable when taught with love and kindness, with safety guidelines and most importantly their interest to want to learn well anything really. Within reason naturally.