I've been working with my granddaughter off and on with the sewing machine for over a year (bought her a machine for Christmas 06) and she just turned 7 a couple months ago.... she is "scared" or "respectful" of the needle as I was upfront and told her how careful she has to be... I don't have a guard for any of my machines.
On her last visit we worked on some needlepoint and she really liked the hand sewing so I think next time I will give her something to hand piece and see how she likes that.
I agree with Patrice, if they want to do it, they are old enuf!