my granddaughters started at 4 (they had already been collecting fabrics and had a good stash :)
i picked up a little singer machine and a little carebear table and chairs so they had work area that worked for them...not trying to deal with my (over-size to them) machine and table.
i did all cutting and pressing; they would lay their fabrics out on the floor, arrange them how ever they wanted and then start sewing them together. i did not take any of the joy of their accomplishments from them by critizing ; they only received praise even when a seam was 2" wide. their project! each girl made a very special quilt for their daddy who is in the military. i even turned a dresser on it's side for them to stand on so they could quilt their own quilts on the long-arm...all 3 of them (now 15, 14 & 10) still sew, and are quite good! the middle child designs purses for her friends and is an awesome hand embroiderer. the oldest makes quilts, the youngest makes pillows and fun stuff...they love to create!
my biggest tip (and lots of people whole-heartedly disagree) is don't sweat the small stuff, let them create without criticism...anything can be (fixed- out of site) to make it work and they feel so (empowered) when they finish that pillow, quilt, rice bag; what ever. keep things (kid-sized) so they do not have difficulties reaching. and let them create. you will learn lots from them.
and as for the stash...my youngest gd is the (worst) when it comes to fabric (really takes after her grandma) if they go to any store and it sells fabric she will not leave the store without a piece (at least a fq) she has been feeding her stash since she was about 2 1/2. when ever the girlcome to visit they know that my fabric shelves are free-they can use anything at all they want to as long as they are making something and not being wasteful...well that youngest girl one time she had a fabric in her stash i wanted to use a little piece of...i helped my self, she wasn't there...used a 4" square from a yard of fabric...well i will tell you what; i was in big trouble when she saw the quilt i used a piece of her fabric in! she knew right away and let me know, her stash was not there for anyone to just paw through! i responded with ... you help yourself to my fabric all the time and i only used a little piece. she said...well you can buy fabric when ever you want...i have to talk my mother into it, and that's not easy!
so, i grin and help their stashes...and i buy my own :)