Oh you are off to a great start. I worked with 4-Her's for years and am now working with my 3 oldest GD who are 8, 10 and 11. This summer they sewed pajama pants from flannel or cotton fabric using a Kwik Sew pattern. They've sewn potholders, pillow cases etc before.
What if you made the coaster a pot holder size using an 8 or 9 inch square? I use old bath towels as a padding. My Grands made them for teacher gifts at Christmas time.
Yes it's so hard to keep your hands at your side! In the early stages, I stress it doesn't have to be perfect and if it's a little crooked on the inside who's going to look as long as it holds every thing together. And that the more you sew, the better stitcher you become.
This is a great pillow case tute and all finished seams
http://www.allpeoplequilt.com/millio...s/RollItUp.pdf
Kudos to you for sharing your skills and love to a new generation.