Take a look at this thread from the QB.
http://www.quiltingboard.com/main-f1...s-t256124.html
I think the first and most important thing to teach a child is how to thread the machine and wind a bobbin. It gives them a quick success and some confidence. Then choose a small, relatively easy project so that they aren't overwhelmed by the sheer size of it.
My grands all started with a 4 patch. I cut fabric as I thought they were way too young to use a rotary cutter. And I had them use elmers washable glue instead of pins, so that there was no fear of poking themselves with the pins.
Have a great time with the 8 year old. The truly important thing to teach a child is to have fun while sewing. If a kid is not having fun, sewing as a hobby will be quickly discarded.