This is for me personally, so take from it whatever you want to. I have 4 kids, who are between the ages of 14-22.
I would NOT try to teach anyone younger than 4 or 5 how to knit or crochet. A child would have to come and ASK ME to teach them before I would attempt to.
Anyone using needles/hooks younger than 4 or 5 could result in serious injuries.