I think some felt projects would be perfect. It's inexpencive and doesn't ravel. Supplies in a sewing box with a project ready to go is a great 6yr old gift. Will you be including lessons?
This (sorry it's not a link) should take you to a felt doll project at Family Fun. (great place for kid's projects)http://jas.familyfun.go.com/crafts?page=CraftDisplay&craftid=10047
A pillowcase skirt kit might be another idea. Or felt pillows or ornaments (with buttons 'cause buttons are fun!)
I'm so excited for your gift!!