I made clothes for one of my DG's while she was living with us (4yr-7yr) then she would come & spend a weekend or week. When she was 8yr she asked for some fabric & next thing I knew she made her Gampy a knee pillow case by hand, that was 13yrs ago & it is still together. When I started teaching myself to sew 1yr ago she was there by my side again. I showed her how to thread machine & wind Bobbin and taped down a 1/4" on my machine. She has now made 3 dog quilts a small lap quilt for a male school mate for his birthday (with perfect patching fabrics) and just finished sewing a Jelly Roll Race top. BUT when it comes time to quilting she procrastinates. I guess because I'm just learning SITD & she hears me getting upset she don't want to do it LOL. So I'm not one to give advice since I'm a beginner too but maybe find out if they have ever sewn before & if so at what level they are at & maybe have a couple of classes for the different ages. Sounds like a lot of fun but I'm with you on the holding my hands behind my back. Good luck & hope you spread your love of quilting and or garment sewing.
Jeri