Knitting and spool-knitting are generally safe for well-behaved kids - but they've got to be the type who don't need instant gratification. Knitting takes a lot of patience. It's not necessarily hard to learn (or so they tell me, it took me forever to figure it out), but a small project can take four hours easily, especially for beginners.
I found a few books for kids online. I haven't read any of them, so I don't know if they're any good or not, but they all have bright, appealing covers, so thats a plus. XD Anyway, here they are:
- "Corking" by Judy Ann Sadler, is a spool knitting book with some finger puppets and similar projects for kids 6+.
- "Kids Knitting" by Melanie Falick, which seems to be standard knitting instructions for kids, probably 10+.
- "Kids Knit!" by Sarah Bradberry, another standard knitting book. Apparently this one has 20 different projects. It's listed for "Grade 5-8", but a reviewer on Amazon said they used it to teach 1st and 2nd graders how to knit.
Regarding age guides... If kids live in knitting families they can start younger. I've bumped into people who taught their kids to knit before they learned how to read. On the other hand, kids who simply have a personal interest in knitting might start later or slower. Ultimately I guess they'll check out the book that appeals to them the most, whether or not they're ready to tackle it. But these look like pretty good starting points.